Hey BigBear - I have (2) Zoom pedals - 505II and the *new* G2 pedal. Not sure how they'd compare to the orginal 505, but the (2) I have are both excellent pedals, with loads of sounds & effects. I use them with both tube and solid state amps, with equally great results. All Zoom pedals have various equalization & depth / rate adjustments, allowing you to "tweak" your sound even further. The new G2 pedal has another really great feature: a built-in drum machine for practice. That, along with some great models of vintage amps and effects. There's a link under a thread that I started for the G2 in this same forum section - you might want to check it out.
The other thing I would mention to you is that buying new would give you the benefit of a warranty vs. buying one from a pawn shop, which wouldn't. It might sound good at the shop, but like any electronic device, they're very sensitive to hard use. With the 505II at around $59 US, and the G2 at $99 US, they're not outer-worldly expensive, either. That extra $$ spent might alleviate the frustration of dealing with a defective unit down the road. Just a thought, for whatever it's worth.
For players who may not want to dive into a full-on modeling amp combo, they offer the average player a cost-effective option for creating unique, usable tones with just about any type of amp.