Magpul introduced the M-LOK family of attachments for popular shotguns recently, and a fore-end for the Mossberg 590 arrived here at the 'Desk not too long along. The fore-end has M-LOK attachment points at the 2-, 6- and 10-o'clock positions for M-LOK-specific attachments such as fore-end grips, Picatinny rails or numerous other possibilities.
Having a few spare moments (ha!) this past weekend, I installed the fore-end on the house Mossberg 590. Attachment was very simple - the tool Magpul includes to remove the castle nut works AWESOME. Aside from removing my own WECSOG* additions from the shotgun, it took perhaps five minutes from laying the 590 out on the bench to tightening the magazine cap after installation.
Should accessories be desired, the M-LOK attachment method allows for immediate installation without removing the fore-end. However, it would only take a minute at best to remove if so desired, or to return the Mossberg to original condition.
*Wile E. Coyote School of Gunsmithing, thanks to SayUncle for the term.