This is the only Boss overdrive (or distortion) pedal I've ever bought (it was on sale at GC for $30). I was in the middle of modifying my TS9 and TS9DX and had been reading about these online and thought I'd buy it. This pedal comes stock with a JRC 4558D op-amp chip (the new version of the magic chip found in some original TS808's) which I found to be a big plus. The pedal sounds similar in a sense to a TS9 808 mod but has a little more hair and a bit more bark. Not quite as transparent as the TS9, thus it doesn't quite make as clean of a boost as the TS9. This could be due to the clipping circuit, which can be modified. For bass application, it makes for a good overdrive; doesn't kill the lows and has a good bark rather then being muddy and sterile. On guitar I'd prefer the TS9, but this pedal does have a good sound (kinda reminds me of an MXR Distortion+). The downside is that it is rather noisy, especially with '57 Classics.
Construction wise all Boss pedals are built well. I'm curious about the noise and want to see if there's a way to clean it up.
This pedal was a steal at $30 (I've seen them go for more then that used). I don't really know much about the Japan vs Taiwan construction, but with electronics the principles and componants shouldn't be too different. Other Boss pedals I've tried have been a bit too plain or fuzzy. This one seems like the red headed stepchild of the Boss family.