Yeah, you have to be careful with that. if you accidentally hit the button you could lock your brakes, either on or off. what I mean is that if you are NOT applying your brakes and hit the button then the brakes will not work for that moment that the switch is hit (the linelock activated prevents fluid from flowing either into or out of the brakes).
If you are hitting the brakes and accidentally hit the button then the brakes will be on until the button is released.
My biggest problem is that I have a t-handle with a button in it - but I use that for the nitrous. I use the button that comes with the little rubber band, and I wrap that around my shifter handle. HOWEVER the button rattles while driving, and it drives me crazy, so I wedge a small piece of paper in it when not in use to prevent it from rattling. Sometimes I accidentally hit the button and because the cardboard is there the button gets stuck in the on position - again if the brakes are being applied at the time the brakes continue to work until I come to a stop or free the button -and likewise if the brakes are not being applied at the time the button gets stuck then the brakes don't work at all until the button is free.
The T-handle is nice, and the button doesn't rattle. Also it takes some effort to push that button so your not likely to activate it accidentally. Go with the button on the handle, the one with the kit is too easy to push and like I said before rattles like crazy.
Hope this helps.