i have one. i have had it a few weeks. i can't compare it to the go-vibe or pa2v2, as i have never owned or used the other two.
i purchased this one due to the design; i like the on/off switch built into the volume control (not a fan of cheesy toggle switches), as well as having the dc jack option, and i wanted something w/ a plastic case.
as far as sound, as i said, i can't compare it to the other two. to compare it to the jack of my zen micro, listening to my koss ksc-35's, the highs aren't as bright and are more controlled, the bass is increased and more controlled. sound is not a huge change, but is enough that i prefer to use the amp.
my choice was between the same 3 you have on your list. my decision was made due to the features, not sonics, as i could not find someone w/ my exact ears and setup to tell me which i would like the best.
as far as the input jacks being close, i use standard mini plugs that come with stuff; i don't own anything w/ audiophile grade heavy duty oversized ends on them. i have the little cardas mini to mini and my headphones haven't, nor will ever be reterminated, and everything fits fine. if you are into having heavy duty cables on everything, you probably aren't into buying 60 dollar amps off ebay...
imo, it's a decent little cheap amp that will make a noticable difference for the better in a fairly portable system listening to mp3's on the go. i'm happy w/ my purchase and have a feeling it will last a long time. what you see in the auction is what you get. the seller puts all his cards on the table, which i think is a good thing.
hope that helps
