OK....offbeat review warning here: we recently made a family trip and I was 1) Glad that we had bought the RoofBag, and 2) Glad that we didn't need it.
When I got the bag, I did do a test installation on our car. The quality appears excellent, all the seams are well-made, and the zipper is covered by a flap that gives me confidence that the bag will resist leaking in almost any storm I can imagine. The shape of the bag is tapered, which should help with wind drag, noise, etc. The material seems like the sort of stuff I'd want on a liferaft if I were dumped in the middle of the ocean, sturdy rubberized stuff.
Also impressive was the thoroughness of the instructions, the welcome to contact the company in case of questions, and the quality of the ratcheting straps.
The only negative I can think of is that the very black material really heats up--anything inside the bag will get really hot on a sunny day.
But my bottom line is that I like the idea of having this bag just in case we need more stuff than fits into our small car, but don't really want the minor hassle of installing it, possible wind noise, reducing our gas mileage, or having our property just a knife's blade away from a thief. I have a lot of peace of mind knowing it's available in case we're packing more than our car will carry. For that reason alone, this was a great purchase.

We bought this for a long trip to go on top of our bare roof Ford Edge. This was hundreds of dollars cheaper than any roof rack option, easy and fast to install and take off, and fit a TON of stuff. We packed nearly everything for a family of 4 for a week in this thing, including a ton of baby stuff. It was quiet on our trip too...didn't even notice it and my husband is very sensitive to noise. We were doing about 80 mph most of the trip and it was totally fine. A great buy!

It's a 500 mile drive to my son's school, and each year we've faced a choice: take my pickup truck and have plenty of room for his stuff, but suffer bad mileage and discomfort for the rear seat passenger, or take my wife's sedan and get great mileage, but face the "10 lbs of crap in a 5 lb sack" dilemma. After all, nobody likes traveling with a microwave oven in their lap, even a small one. This bag let us all ride home in comfort, and despite some additional aerodynamic drag, more efficiently than my pickup.

The quality is excellent. The materal is thick and heavily rubberized, and the zipper is very tight and protected by a flap on all three sides. We used it without a rack and strapped it through the doors of our 2013 Camry. It partially covered the sunroof (which allowed us to see if it slid around.)

We typically run around 80 mph on the drive, and had a strong crosswind for part of the drive. The straps did increase the wind noise, but not excessively. The bag did get pushed back a couple of inches but after that was perfectly stable. Someone suggested a piece of yoga mat under the bag, that's probably a good idea to protect the finish.

The straps were good quality, and the instructions are quite clear and show examples for various vehicle types.

Did not get to test the water resistance. Maybe next time.

This bag holds alot of stuff! I ordered the 15 and I was able to fit a medium suitcase, 6 extra large ziplock vac bags full of clothing, a duffle bag full of shoes, a small laundry bag half full, a makeup case, and a small misc box of this and that.. it was pretty easy to install and fill up..im 5'2" and with the help of a step latter was able to install and fill it without any help..I gave four stars solely for the amount of cargo it holds..im going to do an update on actual performace after we make it to cali..almost forgot im using this on a VW Jetta..no roof racks or side bars..

Update 10/29/16
So we made it from NYC to Central California with no issues with the RoofBag..we drove through pouring rain all of IL and MI..super strong cross winds in NM,AZ, and CA and not one single problem with the bag itself..the only issue we had was duruing the heavy rain there was a bit of leakage in the car but only because i tightened the straps way more than i probably should have..but hey better safe than sorry..i would suggest using addintion straps..i ordered some REALLY GOOD EXTRA STRAPS FROM A COMPANY ON AMAZON CALLED VAULT CARGO MANAGEMENT..THEY WORKED VERY WELL AT holding down and honestly slightly over packed ROOFBAG (dont over pack your bag) with the additional straps in place and driving at speeds up to 95 mph I only had to scooch the bag a little bit back center of the roof one time and that was in TX...I REALLY RECOMEND THIS ROOFBAG TO ANYONE..BTW I was able to fit the following inside my RoofBag..1 medium hard shell suitcase, 7 extra large vacum bags of clothing, 2 small plasic storage cases, 2 medium duffle bags, and 6 large anatomy books..the vacum sealed bags really made a world of difference with the amount that bag was able to hold..i recomend the vacum bags if your really trying to fill that bag all the way up..ok thats it! Grab this bag if you want your stuff to arrive DRY AND SAFE TO ITS DESTINATION

After significant research we decided on this bag because it seemed to satisfy our need and is priced at a fraction of the cost of Roof rack and travel box. Since we will likely use it two or three times a year spending the $120 is much easier to digest than $1,000 for the rack set up. First off, it is pretty big. We used it on a 2016 Ford Explorer and because the roof rack does not have anything to attach the bag to, it was secured through the doors. This results in a slight increase in road noise but nothing too distracting for our 300 mil each way road trip. It did not rain so I can not comment on the waterproof ability. Because the bag is pret be, make sure you do fill it as directed in the instructions. I placed the heavier stuff in the rear section of the bag. We cruised at 74 mph during the trip and did increase to higher speeds briefly to pass a truck or other vehicle and experienced no shifting or bag movement. I must say that I was a bit doubtful of the whole set u, especially with having to attach through the doors, but I am very impressed. Because there can be a fair amount of desbris on the front of the bag after the trip, bugs and stuff, I recommend cleaning it while the bag is full and attached to the car before removing the contents and taking the bag off. It just makes cleaning it easier.