I have the 507 on a Scalarworks mount... I would add them to every shotgun I could.
The circle/dot reticle is awesome and the optics really run. I love the solar option and mine have been 100%.
I am usually a RMR guy through and through but the Holosun's are winning me over. I prefer the 507 on my Benelli M1 over the RMR on my M4... your mileage may vary.