well it's just a rolling belt that feeds it trough so you could call it either i guess ? get one with the smart sand if you can.
The difference in push/pull is where the belt drive motor is mounted.  Standing at the infeed end of the DS, if the motor is right there by the on/off switch - it a push.  If the motor is on the far side of the drum (away from you) then it's a pull drive.

I generally buy rolls in bulk, and cut out my own strips. A lot of paper places offer them. Price breaks down to a few bux a roll, and what I get is X or J heavyweight backed, and lasts about 3 to 4 times longer than the crap SuperMax sells for MUCH more.  If J weight can be gotten for cheap, it is superior in most cases, and usually offers 3 to 5 times the life of X weight, and all of it is a lot longer life than what you get from the name brand material. So if I bought 3 rolls of the J weight I linked to I'd be at 30 bux, and have 3 belts that will outlast the name brand stuff by a LONG margin, fo almost half the cost. Easy Peasy.
I wasn't aware of the X and J weight classification.   I've just been buying roll paper with a cloth backing specification