The best thing about the Silver Bullet (or Block) is the ability to be sure the rear wheels are absolutely parallel.
However, if you can get one, GoatBoy's drilling jig (but with the steel inserts) is much better (as well as quicker) for drilling the axle holes. Another great feature is that it is much easier to drill the holes with one of those hand vices, whereas the Silver Bullet works best with a Proxxon drill. I found it too difficult to use the hand vice with the Silver Bullet.