I have had SM94s, SM81s, and now KSM141s. I have to say I liked them all a lot, but I can't afford to keep all of them, so I kept
the KSM141s.
The SM81 is an obviously better mic than the SM94, but I would say the same about the KSM141 to the SM81, and not everybody would agree. The SM94 isn't bright at all, which is refreshing compared with a lot of other choices in its price range. It is MUCH better than the C1000, which is similar in that both can run off internal battery.
For acoustic guitar though, I would probably pick the SM81. In fact it would win on most sources, other than something like fiddle.
Other pros for the SM94: it fits the same clips as the SM58/57. It's really a very good live condenser for ac guitar, overheads, and yes fiddle
It isn't too expensive and the clip interchangeability is handy. I did several shows with mine on a wide range of sources (choir, bells, piano, fiddle, guitar, overheads, even a play) and was always pleased.