Personally I would't use any mag pump on a beckett skimmer, (but it can be done, just ask David). An external "pressure" pump will always work better on a beckett because of the inherent back pressure from the injector.
It's hard to compare a beckett to a needlewheel. Both are very good designs, but totally different. Both will do a very good job of skimming your tank.
Becketts can take a little more fiddling to tune/keep in tune. Also the beckett injector needs to be cleaned now and then, but that just takes a few minutes.
Needlewheel's are a little more plug and play, and probably need a bit less cleaning time.
Needlewheels usually need to be in sump, the bullet's can be anywhere.
I'd say if you can get a good deal on the bullet, grab it. If I was buying new maybe the G