When playing weekly in our P&W band scenario, I use a Behringer 90w 1x12 w/ piezo(?) tweeter "keyboard" amp as my acoustic guitar monitor amp. I am running into a DI then XLR out into FOH PA, and also 1/4" out from the DI to the Behringer.
Its not a main gigging amp (although it could be used for that), its just so I can hear myself amongst the vocals and other instruments. I have the amp on a stand tilted up behind me, works out pretty well. Been using it in this manner for the last approx. 5 years.
I would like to try the Fishman Loudbox (Mini?) sometime, just to see what its like.
-Gary K