Have used these in the past to patch up a goretex bivvy bag and they have been perfectly good, these i bought for my repair kit, better to have them and need them, than need them and not have them,
First aid kits are a must on the hills, but remember your gear also needs a first aid kit too, it can be as simple as a military housewife kit (spare buttons and thread) youll get these at most surplus stores, spare laces and a couple of patches.