I've only experienced the Glock preamps on the Sandberg basses (and the modified Glock preamp with different frequency settings on the GS5 basses). I've owned and tried the OB-3 on a wide variety of basses.
First, they are more similar than different. They could both be described as more toward the 'hi fi' end of the tone continuum. On both these circuits, the treble shelving control starts VERY high, so that is more useful for cutting upper treble than adding anything useful up top IMO and IME. Also, the bass controls are very deep and wide.
While I don't totally dig either of these pre's (I like the OB-1 and Sadowsy pre much better for my personal tone goals), I prefer the OB-3 over the Glock due to its slightly more meaty tone, and the switchable mid control (the Glock is fixed at 550hz I believe.. not sure, it might have internal DIP switches), which allows you to boost mid mids like the Glock, but also cut upper mids if you so choose).
As long as you like a very pure, relatively hi fi type tone, either of these are pretty darn nice. I wouldn't put either in a J or P style instrument (I find the Glock a very poor choice for the Sandberg J basses), but for basses with big, modern soap bars (like the Groove Shoppe 5 for example), they are pretty cool.
IMO.
