-10 on the posted photo with the "Fruit of the loom" tighty whities! UGH! Pleeze!
Shocking taste... Presumably these are converted gun cleaning rags, but still... 
OP: Personally, I do not favor the type of action slide that your Marine Mag. 870 came with. In my view, it inhibits unloading the shotgun in the safest and easiest way. It does impede pinching the hand between the receiver and the fore grip, however, and is most favorable for a very short person using the shotgun. So it may be worth keeping in your particular case.
As for your "now what?" question: Go get a wonderful sailboat and put that bad boy to work as the "boarder repeller" while you sail around interesting and exotic places!
I found that a six-shell side-saddle badly unbalanced my 870 shotgun. I don't care for them much, either. In my case, I opted for a four-shell version as a compromise. I favor a light on a defensive long arm, even if it has salient trade offs too. Basically, for me, it is a question of simply having a light handy should one be necessary. Also a means of identifying a threat or a non-threatening situation. I've got the EOTech/IFL light/action fore grip installed on mine. The front end finger stop'll bite ya if one is not careful...