Can I safely and effectively use my small Vox MINI5RCL Battery Powered Amplifier, Classic, 5W, 1 x 6.5" for an acoustic-electric guitar or should I really buy like the Yamaha desk acoustic amp? I've read you can use an electric amp but need to have a mixer and I haven'r a clue about mixers or pedals -- I just love this little practice amp over any other I've used for my electrics and wonder if I have to shell out $200 for the acoustic Yamaha -- which actually looks and sounds pretty cool and I'd wait for a sale if I need to. I am not, obviously, a professional musician, nor will I ever be. But like many other retirees -- I've returned to a love from the distant past and am enjoying not only the playing and the music -- but all the wonderfully accepting folks I have met returning to music. Thx
Uh, anything wrong with trying? If you are 500 miles from the next music store, just bring what you have with you and try there. Of course, to keep the decision open it might make sense to save enough money in case you do want the amp. Or decide which one it is going to be and, in case you really need it, get it by mail order (and very much preferably from the shop that let you try it!) once you got enough money.
Most amps will have enough inputs for a single guitar or even two. It may just be that they are unsuitable for the kind of pickup you have on your acoustic, and of course the sound might be unsuitable. But you won't find out until you try.
Can I safely...
yes, sure; everything sold today as guitar equipment is compatible with any guitar, in the sense that you won't break anything when plugging one into the input.
depends on what you call “effective”. For starters, 5 W is of course not a lot – while it is enough to get pretty loud sounds, this relies on the compression you get with a decent amount of overdrive. Even a “clean” tube guitar amp produces quite a bit of this. But for an acoustic sound, you'll want it completely clean, and then that amp probably won't be much louder than the guitar itself.
The sound itself will probably be ok-ish, since the Mini5 is apparently not a guitar amp in the classical sense (i.e. with a fixed, strongly nonlinear response through the cabinet) but essentially a compact broadband monitor with DSP guitar-amp simulations. Thus if you switch it to “line” mode, you should get a reasonably clear sound – provided the guitar pickup is any good, of course.