A slight fidelity bump is to be expected on newer/better hardware, but the "Legacy" effects are exactly why I still have my M5. I snagged one for about $100 new only a couple months before the HX Effects hit, and it's what pushed me to get the HXFX. But the M5 still too good to get rid of. My absolute favorite chorus in the Helix is still the Dimension, which was an M series model. The Particle Verb is also a personal fav, particularly 100% wet.
5sg.
My M5 is unsellable sadly. There is something wrong with it where the far right knob won't turn to 100%, makes some of the pitch effects unusable. I've tried using midi commands to max it out, but it reverts back to about 98%. It also has that grounding issue that is common where I had to remove the screws. It looks nice on the shelf next to my M9 that passes audio and effects but the screen displays nothing.