I also had the Dean Markley for my 12-string and it was OK but hardly very acoustic-sounding. It works much better in a friend's 6-string now, but it's a compromise, not quite semiacoustic-feeling but not purely like an acoustic either. Nice for blues, though.

I put a Fishman transducer on my guitar (under the bridge bone) and it was rather easy to install after all with very basic tools, almost just a knife, a couple of drill bits/battery drill and some sandpaper - just need to work carefully - and it worked very well for acoustic tone. The only drawback is you really need to watch your right hand slapping the bridge with these piezo things. Plus attaching the preamp was difficult/can require a lot more work and cutting depending on the model.