Haven't fired the M249, but have fired our C9. Highly similar. It gets old quick. If you have it for extended periods of time, you'll learn to hate it. Just because it's not as small, agile and easy to carry as a C7 (service rifle). Firing it is pretty fun, though. High ROF with little kickback and pretty good accuracy. Cleaning and maintaining can be a bitch, though. They can be clean as fuck and jam like a cocksucker-even in the perfect scenario. Went out and shot last weekend, two out of 6 guns jammed on one relay, but then again, we were using normal mags instead of box mags, so that was probably the issue.
If you're up for struggle and annoyance, but would find laying down some good firepower rewarding, go nuts.