amPlugs are Great!
So I have two of these little guys: an Acoustic and a Bass amPlug. For what they're worth, these headphone amps do their job!
I bought my Bass amPlug to play at home and not disturb any of my relatives. The Acoustic amPlug I bought for school so as to not disturb my housemates.
The Bass amPlug gives you nice clean bass tones but can also dial in some nice chunky tones as well. Haven't played around with it much for slapping though.
I bought the Acoustic amPlug for use with my Traveler Ultra-Light Steel-string Guitar. It really brings out the nuances of the strings, from the attack to the release (I play fingerstyle). The "blend" option gives you a nice bright and shimmering tone and allows for much more than just the normal acoustic tones of the guitar.
All-in-all, I'm very happy with these headphone amps because they do what they're supposed to, and they do it very well!