I had one on my Remington LTR (.308). It worked OK when I was still teaching myself (by trial and error!) the in's & out's of varmint shooting. It certainly assisted in in taking magpies & rabbits out to 350 yards etc. But now this same rifle is a 6BR and I only use a rear bag. I think monopods are great on the range, but in the field a rear bag of practical size is better and faster; especially when you have a lot of other stuff to contend with when setting up for a shot (lazer distance, wind, angle, dialing it all into the scope, position, hold, etc). The Mono-pod I felt was a little fiddly. Where the rear bag is 'instant'.
....But I still have my mono-pod somewhere, and who knows I may use it again sometime, but probably only on the range.