Its not true bypass, but it sounds fine in-line since it has a nice buffered output, plus its a *killer* pedal to have at your feet...mine has worked fine for years.
I hear a slight difference between the "output" and "bypass" line-outs.
http://www.geocities.com/nobody_upstairs/BossTU2.JPG
The "output" sounds a little clearer, and will allow the sound to be *muted* while you tune...this is the one I use.
The "bypass" keep the sound on thru your amp while you tune, and sounds a little more muffled for some reason to my ears...its weird, but its there and I hear it.
The pedal also doesn't work well at all in an fx loop unless your fx % out is dialed-in high. Best really in front of amp for this pedal.
What else...hmm...easy to read red LEDs in sunlight, and the "strobe" function is *cool* as hell and makes tuning pretty damn accurate.