When getting ready for the New Mexico Off-Road Runner (400+ Miles Bike packing Ride) I was looking for ways to carry water on my Cannondale 29er as it didn't have any mounts for water bottles except for one. I found these at the local Walmart for under $7 and was skeptical due to the price. They mount to the bike with Velcro and have rubber on one side to keep them in place. I put them on each side of my forks and one on each seat stay on the rear of the bike.
I trained for several months with them and after some adjusting here and there, they seemed good to go. The real test came on the actual ride. We had all kinds of terrain to cover and some of it was super rough, which tested these things to the max. They performed flawlessly and stayed put with no issues. You can change the actual bottle cages out if you wish, which I would recommend as these are plastic and cheap, but did surprisingly well. The mounts have eyelets which you can change the bottle holders like any normal bottle mounting system.
Tip: Take bolts out and put on Blue Locktite on threads to make sure they stay put. I did have one back out but the Loctite fixed the problem.