Yamaha GB-100

It's your basic 7-band EQ, 50 100 200 400 800 1.6k 3.2k frequencies and a level slider. Controls are all from +15 to -15 (i'm guessing dB). Of course, like with any graphic EQ, you need some time to get it to work for what you want to do. Input, output, really simple.

I used it with Jackson guitars with Duncan pickups into a Marshall 6100 or Crate BV60. It's noisy, like all EQ pedals, and colors your tone, makes everything sound dull and lifeless, very disappointing. I guess rack EQs are worth the extra money. The sliders all have a significant effect on the tone, but it makes everything sound worse, so cutting or boosting frequencies doesn't help, i would rather have it out of my signal path, i'm better off without it. I tried on numerous occasions to like it, in front, loop, different amps and settings, but i never liked it enough to use it on a regular basis.
I never used it with a bass, though, might sound better, i dunno.

It's built solidly, no complaints there, although the input jack needs to be held in place or the sound cuts out, i'll fix it before selling it. I guess the previous owner wasn't careful enough, pulled on the cord or something. I don't think it's a problem with the construction itself.

I have no idea.

It's a bass eq that i used for guitar, the sound isn't terrible, but just having the pedal in your signal path greatly diminishes the quality of your tone, so it's useless. I've been playing 7 years and i can tell if something sounds bad, maybe not everyone notices that, and it probably depends on your gear. It's a bit worse than the Boss EQ, that i dislike too. I haven't found a good eq pedal anyway, maybe i'll try rack someday, in the meantime,i live without it, and that's ok.