I'm replacing the shower plumbing in one bath. There are two scald methods out there: temperature or pressure. Temperature costs a lot more. Is there really a difference when using a valve with independent flow and temp controls? Which kind of cartridge is best?

The bath that backs onto the one above has a tub hot and cold faucets, spout, diverter for shower. Is there a scald unit for that 2 faucet system? I can access this bath from the back to install it. Don't want to disturb the tile. Also have seen conversion to single valve accessed from front with trim covering the damages. Thoughts?