M4 is really bigger and heavier, but it uses AA batteries (a bonus to me). If you can live with cr2032 that last 4+ years or you have to have a AA unit that last 6 years go with the m4. I chose the micros, still lovin it.
Assumption is the mother of all ****ups.
Know what you know, Know what you don't know. -Paul Pedzolt
"Jack of all trades, master of none, though oftentimes better than master of one" -Mynshul