Installed in 2012, still going strong. 2007 Chevy Malibu, install was easy-ish with basic hand tools. Took about 2 hours total to get working, then I came back and installed it 'professionally' by drilling a hole for the switch and plug.

I went through 3 or 4 FM transmitters before finally figuring out that they're consumable.

One caveat is that it decreases the quality of stations near the set frequency when it's on. I leave it on 99% of the time, and just switch it off if I'm trying to pick up a station when driving out of town.

I really wanted to be able to access the tunes and podcasts from my phone, but I didn't want to get a new head unit and spoil the aesthetics of my old car. This turned out to be just what I was looking for, and I'm 90% satisfied (so this really should be 4.5 stars).

Pluses:
Installation was straightforward and simple. It took me ~30 minutes to get this set up.
No need for the switch: I can cycle through the radio stations without having to flip the switch to turn the modulator off. Doesn't seem to affect the audio quality, YMMV though.

Gripes:
The bass can get muddy. This may also be because I have this hooked up to a bluetooth adapter (Kinivo BTC450 Bluetooth Hands-Free Car Kit for Cars with Aux Input Jack (3.5 mm) - Supports AptX).
Volume is lower than radio signal. There's a way to tweak the gain but I couldn't ever get the volume loud enough to match the radio.

Aftermarket stereos are a theft target, as I found-out in my 1998 Ford Econoline. Put the stock AM/FM back in but wanted aux input. The regular FM transmitters all . . . perform poorly. This seems to work great. Would like to have more than two frequency options, don't know what happens if I travel somewhere with station on the selected frequency. Also, I have the unit installed behind the radio, so can't switch frequencies without disassembly. Didn't see many options that would address either of these concerns though. Be careful with the gain-control pot--it is a flimsy surface-mount component, and when I went to adjust it with a micro-screwdriver, it broke. I had to open the unit up and short-out the contacts (basically setting it at "full" gain). That is working, but a slightly more robust design on that component would be nice.

Do install with the power switch, you want to be able to turn it off when listening to broadcast FM. (Although, oddly, a couple stations seem clearer with it on.)

Not bad for what I needed. My truck's radio don't come with an aux in. Replacing the radio wasn't an option because of the built in video system for the rear passengers, so this seemed like the best inexpensive option. Once I recurved the unit, and the antenna adaptors, I was ready to do the install. It took some experimentation to find a power source, bit once I did, the rest went smoothly. As long as sound is coming through the unit, it sounds good. Really, the only complaints are...

1. The unit only gets about half as loud as a normal FM station, or other source (CD). Beyond that, works good.

2. The gain adjustment and the channel selector are sunken in a little too deeply to be accessed easily. I had to carefully youth the unit to adjust the gain, and the channel selector.

Beyond those issues, the unit works OK. Deducting half a star for each, considering they aren't major issues.

Fairly easy to install, generally works well, and sounds perfectly clear while it's working. It's definitely worth the price. However, I had to knock off a star because it seems very susceptible to interference. There are certain areas I just can't drive through without it cutting out to static; normal FM reception and the rest of my car's electrical systems are totally unaffected in the same places, so I don't have any idea what the problem could be, but it's absolutely consistent.

The only other issue is that after 20-30 minutes it starts getting progressively more staticky, only "resetting" once the car has been turned off for a few minutes. However, I don't know if this is a problem with the device in general, a flaw with the one I received, a problem with the way it's installed, or a more general issue with my car (I haven't noticed any other electrical problems) and most of my driving is just around town, so it's usually not an issue.