The Trigger Treadz aren't something I thought I would ever need on the Xbox One controller, but they are an incredibly useful addition. The Treadz themselves are easily attached (as long as you make sure the triggers on your controller are clean and dry) and are simply sticky on one side. I have had mine stuck on for a couple of months now and they are still sturdily attached.
The grips are useful for general use, but are especially good in games that require you to hold down the trigger, like driving games. I highly recommend the Trigger Treadz, and even more so due to the fact there are two sets in the pack!