Review on Corki Cycles Bike Water Bottle Holder, Lightweight Bicycle Water Bottle Cage For Road Bikes & Mountain Bikes - Red - 1PACK by Nicholas Dobson

These would be perfectly fine for smooth tarmac road riding, but they are not secure for gravel / MTB. Where I ride there are lots of gravel roads so "road" riding usually ends up with at least some mild gravel. I had a bottle bounce out of these (somehow magically onto my foot so I was able to place it back). This was on a gravel road and I don't think it was particularly bumpy. If you want a light weight plastic cage and won't hit bumps these are fine, but if you head towards a bit rougher stuff you'll want to get a more secure cage.