I've tried the split clip feature of the custom particle setting on Particular, and I've never got this to work for me. The spit clips don't play at the right spots...it seems to flicker between 2 adjacent frames when picking the start frames...and with the setting "play once" they don't freeze at the end, the particles just disappear. I know this is not a frame rate mismatch because I prerendered the particle clip to check that. I've seen a few others complain about this problem, but for many others it works fine. I'm on a Mac, by the way.