I use them all the time... usually new construction or remodel, but I've pulled drywall off walls a few times to head out for them too.  For the Frame TVs it's important for the wall surface to be really flat so redoing the drywall is an opportunity to get it right.

Here's that wall showing the head-outs in the framing for the backbox:



This was a double framed wall, so I did a "box-in-a-box" and modified the TA500 so a 14" VersaBox could be installed into it to make space for a WattBox and a few other pieces so everything was hidden when the TV was pulled out:



Recently set a TA500 into a concrete wall by installing it on the inside of the wall form and concrete was poured around it: