I think the newer pricier version takes a umarex 8 shot disc magazine for pellets, and has a round plastic mag with a magnetic centre which can hold metal bb's. You can also half cock the hammer by cocking the slide, but only the rear half of the slide moves - because the front half of the slide moves forward to accomadate the magazines.
The older cheaper one just took metal bb's, and had a completely motionless slide, the bb's going in the pistol grip magazine that holds the gas.
Toilet trained since March