I'd shun technology, personally. http://beardtrimandgroom.com/how-to-trim-your-beard-with-scissors/

I once bought a pair of mechanical trimmers at a garage sale from a really old dude, these can be found on ebay (vintage status), or new. I've never used it, but figured it would be useful at some point in life...

I've got a pretty thick fast growing beard, and I keep it groomed with just scissors until I want to shorten it, then I use clippers.