I've used the same screw in T fitting for the copper pipes here for my water filter under the kitchen sink and for another Mattamy home for their cold water line to the fridge. I haven't any problems or have heard of any problems on these installs.
Tim
PS the guys for OZZ when the installed my kids water filter upstairs, used the plastic compression fittings on the smaller copper pipes. It should be somewhere on my site, although my install of my kitchen water filter install is not...OOPS
