I think DBMs are great for making loading and unloading your rifle easier and quicker.
At the end of the day you just press a button and all your magazine-held cartridges come out in a self-contained unit. You don't have to cycle each round through the action or fumble loose cartridges coming out of a hinged floorplate. I drop at least one round out of my model 70 just about every time but maybe I'm just a butterfingers.
As for the idea of it getting lost or falling out well I don't think those are likely to happen. A fully loaded mag falling to the ground should make quite a bit of noise and your gun will feel noticeably lighter in the off chance it were to just "fall out." I don't think anything is more likely to hit the magazine release button than the floorplate release on most guns like the model 70 that have the button in front of the trigger guard. I've never had my floorplate come loose so I don't see how a DBM would be more likely to have it happen to it really.
As for forgetting it I don't see why that would be an issue either. Leave the magazine in your hunting pack, no reason to take it out. Go as far as to always have a spare loaded mag in your pack even. In fact there's no reason to take the cartridges out of the magazine. There is a misconception that leaving magazines loaded will weaken the springs but that is just not true. Springs do not wear by being under tension, they wear by compressing/decompressing. So in fact continuously loading/unloading a magazine is worse for it than leaving it loaded. The only case where a spring will wear under compression is if it is compressed too far and this should not be an issue in a properly designed magazine.
I don't even own a DBM equipped rifle (besides an AR15) but I don't think that the arguments such as those I listed above are really valid in opposition of them.
