I don't have a ton of experience with arps, but I dig this one. I wanted an arp that I could actually play, as opposed to inputting the notes before hand a la EnergyXT's arp, and this one does that.
I especially like that arp2midi can send cc data as it sends arp data. Lots of fun to have resonance or frequency change in sync with the arping. I haven't really dug too deeply into the gate sequencer features, I've pretty much simply used the arp features, but from what I've read in the documentation this functions can be used to created syncopated rythms against the rythm of the arp. Looking forward to trying this some time.
I haven't heard a lot about this one on the board, and I am the first and so far only review, but I'd be really interested in hearing from folks with more arp experience what they think of this one. At $5 it can't be beat. Maybe that low price has kept folks away. The GUI could be improved a little I guess, but what do you want for $5.