IMHO the Zeller is more of a long range sniper rifle (perfect for fog free maps like Port Bavaria)  since its high damage compensates for the damage drop over long distances.

It's also fun blowing up infantry close to motion mines using the Zeller !

I use the Zeller on most maps since its easy to mask my position using the firing sound (stock sniper rifles have a unique firing sound to them) since I'm always on the move. Oherwise , stock rifles are better for their larger magazine capacity and larger scope view.