definately get the jjos if you can afford it. there is also a free version. the free has less features, and was before some advanced enhancements. You can try all the versions for free (just cant save) and if you dont like it, you can go back to akai os. if you like it, you can buy it.
jjos2xl is what i rock with my mpc2500. I seriously can't live with out it.
I've owned and used lots of mpcs, 3000,mpc4000,2k,2kxl,1000. and mpc2500 with jjos is my favorite.
the reason alot of mpc users like jjos is because he responds to user feedback and is consitantly improving it, updating it, and bug fixing. unlike akai os.
don't be streesed bout it tho, you can get most everything done with regular akai os no prob, but imo its worth the extra quid. especially for chopping samples.
its not auto chop that jjos has. fuck auto chop. its NDC chop (Non Destructive chop). there are markers on your sample you move around with out destructively slicing up the sample. you assign the markers (chops) to the pads, then you can go back to the trim window and move the start and end points of the markers around.
its like zones on the mpc2000xl or regions on the mpc4000, but better because you can have overlapping chops, and there is pgm mode inside trim window so you can preview each pad together...........like on mpc2000xl zones, you can only mess with 1 zone at a time, on jjos, i can be in trim mode, have the beat playing, adjust start and end points of one chop, press the the pad another chop is assigned to, and start adjusting that one.
for those use to mpc2xl chopping and 4k chopping, its a dream come true to be able to play your zones with the beat, while adjusting them. atleast it was for me.
peace.