As for their function on real hardware, I've played what I believe to be the most current versions (as of about two years ago, when I played through all of them) of CE, FoE and Prophet's Guile all on a real SNES via my SNES Powerpak. Crimson Echoes and Prophet's Guile are terribly broken on real hardware because they will freeze/crash in numerous places with no way to progress unless you want to load your save into an emu and play past the broken portion. Good luck doing that with a repro cart. I did manage to finish Flames of Eternity on my SNES though. I don't recall if there was anything impassible or not. IIRC the music was screwed up on all three hacks. It sounds like some of the songs that were altered sometimes loaded SFX instead of instrument samples.
As soon as I find my collection of ROMs that includes these I'll give it another shot. I remember enjoying Prophet's Guile. Nothing spectacular, but worth playing at least once for a CT fan. It's been too long for me to remember much of the details but I thought I remembered liking Crimson Echoes more than Flames of Eternity. Both were good enough for me to play to completion, but had I not been a CT fanatic I'm not sure I would have cared to go that far. I don't recall anything too special about the gameplay (unlike PG) and the story was a bit ridiculous and "all over the place" at times.
Oh and a speaking Crono is blasphemy.