Not sure I understand where people are coming from in this thread. For what it's worth, I have both ER32 and ER25 chucks and collets for my Myford (ML7), The chucks simply screw on to the Myford spindle nose thread. No "backplates" are involved and certainly not 4 or 5 inch ones. I believe mine came from Chronos
The Arc ones appear to be mainly directed at the Minilathe market although, I guess you could adapt them with a suitable Myford backplate but it seems a pity to go through two mounting interfaces instead of one.
Incidentally, I don't prefer either one (ER25 or ER32) over the other. I wouldn't want to lose either one. On the mill I again have both sizes but rarely use ER25 and could do without it if I had to.