Friends told me about this last week, so I signed up and used it yesterday. It was great! I verified in about 3-5 minutes, and was easily able to find bikes. The seat was ripped on the 3rd ride, but there is a way to report a problem at the beginning of the ride so you don't get blamed for damages.
I do wish there was a way to adjust the seat, as I am only about 1.6 m and it was a tad on the short side for me as well. I rode about 16 km throughout the day, so someone taller would have a hard time doing that without killing their knees.
You can't unlock more than one at a time, and I did find that if you don't have your app open when you lock it back, you don't get to report on the location and do the photo for points on your account. There's no way to go back and add it, either.
There aren't any gears, so it can be difficult to keep up with people on their Giant 18 speeds. The brakes worked well and there was a bell that was easy to ring as you were riding.
I'm defninitely a fan!