If you search on this site there has been a lot of good discussion on the Benelli M4. I was always curious what pros and cons there were that would come to light with a large deployment.
Your description of requiring maintenance seems to me to explain differences in opinion on the M4. Position shooting with slugs has got to be a painful experience especially in prone.
To get back on topic. I have an Aimpoint H1 to experiment with on a Beretta 1301. I think any dot sight makes it so much easier to place slugs on target.