All 24 of my engines have been BPRC'd. I think the last was a Williams brass USRA 2-8-2 I repainted for a class of engines Atlantic Coast Line used:
I gutted the old electronics out of the engine except the motor. Installed a Deltang receiver, a 9.6v NiMh battery pack inside the tender shell, with an On/Off switch and charging jack module from RCS Australia under the foam coal load in the tender. The headlight and rear light are LEDs.
I've had no problems with signal loss running around my 13x30ft layout. My steamers range from a small MTH USRA 0-6-0 to a massive Williams 4-8-4 N&W class J.
One thing I haven't seen mentioned is how to connect the electronics from the tender to the engine. Depending on what type/brand of connector I used I usually have to fiddle with the existing space normally used for mounting the original connector. Sometimes there's no issue and sometimes I've had to Dremel some material away to make the new connector fit. I've used original connectors (Williams and MTH) and have even put together my own.
Diesels have all the electronics under the shell and no need for a cable. My tightest fit was a MTH NW2 but I managed to stuff it all inside and even put an interior of sorts and crew in the cab.