The Loudbox and Loudbox Mini get great reviews, but I don't have much experience with them. I don't see why the Mini would not work as plenty of stage monitor while something else handles front-of-house (FOH) coverage. It might even work for the whole room too.
I used to have a pair of Mackie SR-450's. They are very clear and accurate in tone, kinda like overgrown studio monitors, but are bigger than you mentioned. I like the 450 sound better than the smaller SR-350's, as much as I really wanted the smaller speakers to work. These days, we mostly use a Roland AC-60 and / or an AC-33 (battery powered) box for small to medium venues like a coffeehouse. The newer Roland AC-90 has a bit more power still, but we've never felt the need to upgrade. It depends on your needs and the size of the room you intend to fill.
For large venues and outdoors, I have a Mackie PPM 408 powered mixer driving two pairs of Carvin PM5 passive monitor bookshelf speakers.
http://www.carvinaudio.com/products/pm5-b-program-reference-monitor-blackThe Carvin's are light and sound good too, and with four of them spread out we've successfully covered a 300 seat re-purposed movie theater - with a balcony. One of the four can be turned back toward us as a stage monitor if needed.
Between all this equipment we can handle anything that we are likely to encounter, including outdoor weddings and up to a 300 seat theater. Venues that are larger would have their own PA system and stage monitors, and sound tech. We are generally an acoustic guitar, one voice, and a mic'ed flute. Sometimes we have an extra guitar player or a bass too, but not often. Hope this helps.