I ordered the BBS02 Bafang mid drive kit with 42 tooth ring gear and 13 AH 48V shark battery with EKD01 display. I am very pleased. I installed this on my 1990's Trek 750 Multitrack bike. The kit was easy to install. It took me about a hour to disassemble my bike and get it ready. Installation took about an hour and then the first test ride. Later I spent another hour cleaning up the wiring and installing the free headlight.

It does not say this anywhere but I found the controller turns on the headlight by holding the gear up button for a couple of seconds. Hold it again and the light goes off. I used to use my bike to commute to work and had set it up with narrow 700x28 tires for low rolling resistance. On my first ride I put the bike in the top, highest gear and set the controller to position 1. I found that the the power output is very strong and the bike quickly goes to 15mph with little peddle effort. In setting 2 it goes to 20mph with little effort. In mode 5 it's 30 mph. This system had more than enough power.
I have ordered the programming cable so I can detune the power settings. I can see from the display that upon starting out that it is sending out 500watts of power at startup when I only need 100 or 150. I do still want some exercise when I ride. I totally understand wanting this much power if you are only using the battery to propel you. I am goes to change out the tires to something with more sidewall flex like a 700x48 to take up some of the vibrations that come with the higher speeds that I will be traveling at now.

I did order the and Install the Gear Shift Sensor. I recommend this if your bike has more than one gear. If you only have one gear, you don't need it.

Overall not a complicated install and I am very happy. Looks like I will get around 50 miles or more per charge at an average speed of 20 MPH.

Pros:
- Very strong motor

Neutral:
- You lose the ability to have multiple front sprockets and therefore available gears but now you have a motor so.....
- Depending on your bike frame this likely will need some creative modification for wiring or battery placement

Cons:
- Definitely not a natural feeling while pedaling. The motor engages too strong when assist is on.

I purchased the 44T motor with the 20ah shark battery and put it on a low end 21 speed Shimano mountain bike. There's definitely a degree of mechanical know-how that you need to do this conversion but there are enough videos showing how to remove the various components where it should be manageable for most people.

For cord management I ended up using electrical tape instead of the provided zip-ties. This kept the wires cleaner and if you don't mind seeing tape can better secure it to the bike frame. There was plenty of cord provided and at times I had to wrap it around the frame a few times (I spiraled it) to take up the excess.

I had to buy a few extra things to make this work. First I needed to get a tool to remove the bottom bracket (what the front sprockets attach to) https://www.amazon.com/dp/B09KV4PRCF?ref=ppx_yo2ov_dt_b_product_details&th=1. Second, the battery wouldn't fit between or underneath the frame so I had to buy a rear tire rack to mount the battery on. I did get the largest battery so I assume the others were smaller and it might not have been an issue.

Once it was put together, I turned it on and the C961 display was giving me an error. The pedal assist and throttle still worked but I had no idea what assist setting it was on. I unplugged the display and everything worked normally after plugging it back in.

As for the performance.....wow. The motor has a lot of torque and crushes hills. In the lowest gear (now only 7 because you replace the front sprockets) I have to be careful or the front tire wants to come off the ground. Before the conversion I could barely pedal up my driveway in the lowest gear while standing up and throwing all my weight at the pedals. After the conversion (lowest gear is now a much higher ratio than before due to losing sprockets) the bike slows but easily crawls up my driveway. That being said, as soon as you start to pedal the motor takes off even when you're on the lowest assist setting. You basically have to turn it off if you want to go slow (like in a crowded area).

Overall I gave this a 4 out of 5 solely because I haven't had it for very long and also haven't been able to test the battery life or overall durability.

Easy to install if you know your bike. Shouldn't install it or have it if you don't know your bike. I didn't heed the warnings or really care enough to look into safety. On my first ride after installing I, took a turn going way too fast and couldn't get it tight and slammed into a parked SUV. Bike went under the SUV but still managed to destroy my back rim. I was destroyed also with 4 broken ribs and a bruised kidney. 3 weeks into an 8 week recovery. I will ride again.

Make sure you consider the fact that you are converting a bike into a low speed motorcycle. I did not respect the power so the power taught me a lesson. Just be carful and avoid my route. The wheel is on it's way and I'm a couple weeks away from riding again. Respect the speed and also remember it is still a bike from a safety standpoint. Don't exceed limits and remember this is not a speed motorcycle or Harley and the motor is added to this pedal configuration. It is no where near as agile or grips on the road the way a solid motorcycle does today. Play it safe until you are very familiar w how it operates after installation.

Back in the late 20th century, I was in really good shape and rode about 2,000 miles per year. I hadn't ridden a bike in 10 years due to arthritis and chronic tendonitis in my knees and ankles. I installed the kit on my old cyclocross bike. If I had to purchase the kit again, I'd get a smaller battery that fits in the frame rather than the rear rack-mount. The battery is heavy, and although it doesn't pose any handling problems, a frame-mount battery would definitely help keep the center of gravity lower. The brake switches (cut power to the motor when brakes are applied) that came with the kit aren't compatible with road bike levers nor is the throttle, so I didn't install them and after a long shakedown ride I have no concerns. If you're installing the kit on a hybrid- style bike with a flat handlebar, the brake switches and throttle should fit perfectly. A shift sensor (sold separately) is a must, as this kit makes LOTS of power. The default assist levels are a bit too aggressive for my taste, so I'll be using the programming cable (also sold separately) to decrease the assist (level 3 assist is plenty, level 5 is REALLY fast). Overall, this kit is superb!

I'm a mechanically inclined person, but called in a bike tech to assist with install. We both agreed after putting in the drive and then realizing the brakes wouldn't work that buying is better than building an e-bike for the average biker who isn't also a Bike Tech. If you do buy a retrofit kit, for safety reasons, make sure your bike has great brakes; my coaster (backwards pedal) brake is incompatible with the Bafang & due to my fork and frame I cannot add caliper brakes, so I returned the unit.

For returns:
*the battery is HEAVY and lithium - expensive to return.
*you will be paying for return shipping (battery + Bafang was $100 to return via USPS); I recommend buying a battery only after successful install
*keep track of how things were packaged, as you'll need to put them back in the box in the same way- and the seller requires photos of all UPC codes on inside packaging as part of your return.

All in all, I'm out about $250 for this failed experiment, but that is cheaper than a visit to the emergency room because I couldn't stop my bike.