I would like to set up my tub faucet with 3 cross handles--hot, cold, plus diverter for a handshower. I am told that this configuration is not up to code and that I need to select a one-handle faucet or install an anti-scalding valve. I did a search and found remote pressure balance valves that say "For use with exposed or concealed non-pressure balanced valves where temperature maintenance monitor is required." One of them looks like the link below. Will this solve the issue, and do they work for any faucet (some literally say, "pressure balancing of any faucet or retro fit")?

Here is a link that might be useful: Grohe inline remote pressure balance valve