A carbine can take on either of two similar meanings:
1. It is a shorted version of a rifle shooting the same ammunition. This would be like the Army's M4 compared to the M16.
The more traditional definition...
2. A shortened rifle that also shoots a lower-powered cartridge. An example of this would be the M1 carbine. It is a small rifle that has its own lower-powered round.
I can second what Kel said, but for slightly different reasons. A 9mm or .40 cal pistol round is not going to be very accurate at much beyond pistol ranges, even out of a rifle (I would question their 150m statement). A .22, however, is high velocity and keeps good accuracy out to 100 yards. And, ammo is much less.
Once you've learned to shoot, their SU-16 would be a good step into a higher-powered cartridge in a fairly small package.
But, if you have the money, go for it.
