They are fun but they aren't very accurate.
I have one and its realisticly weighted and balanced. I use it for practicing my presentation skills and for making the first shot out of a holster. They have a bit of umph behind the plastic pellets- enough to puncture a paper target at about 15 feet or so, but are wildly inaccurate especially beyond that distance as the pellets curve all over the place.

They are not copatible with BBs- they fire 5mm plastic pellets (IIRC), and BBs are around 4.5mm.

The cheap airsoft have to be cocked by hand with every shot, ,like ht eone I have. More expensive ones run on batteries and can fire in semi-auto and even full auto modes- some of these are as expensive as the real semiauto firearm they replicate!