Progressive Industries' EMS units are very good.
If you have a 50A coach, you should get a 50A EMS unit. If your coach has a 30A shore power connection, either one will work fine, but of course the 30A one is less expensive. (The only reason I can think of to get a 50A one in that case is if you might upgrade to a different RV and move the EMS over to the new one.)
If you don't need the remote display or its bypass switch, this would be a great choice. (If you want to mount the EMS unit where you can't readily see the display when needed, the remote is very much recommended.)