Saw an ad in a magazine last night for a new model Remington shotgun. The 870 DM. It has a 3 or 6 round detachable magazine, which I suppose is what the DM stands for. Looks like a regular 870 in every other way only without the mag tube.
There is also the fact that the only shells that will stay reliable when loaded in the mag for any time are full brass shells. Plastic hulls will deform quicker in a box mag than they do in tubes. I agree with FL-NC, I'll stick with my tube mag 870.It seams like a good idea to me especially if you have a sidesaddle and a +2 extension on your 870 . This would cut some weight and you would have a faster reload . I haven't held one yet , but it might even handle better with the weight of the shells not being in a tube .