If a TPC400 is anything like the IC Controls units, of which it was derived from, these devices are more than a simple on/off devices. They have over-current protection, and can be switched to CONVentional mode from the remote, unlike PowerMasters that you have to walk over to them.
I bought three separate IC Control units, and they changed the firmware in them (I read the manuals, silly me), later units could control some MTH PS1 features (in CONVentional mode) . I would assume the TPC400 would get all of those improvements.
I would have to think over which is better for a traveling layout. With a PowerMaster having two less wires to connect would seem an advantage, on the other hand, anybody could come with a CAB1 or CAB1L and monkey with your trains. You could in theory have the TPC400 hooked up only to a personal computer, but I don't know of anyone that does that - this would mean you would have to go over to the computer to cut the power in an emergency, sounds like a pretty big downside to me.