Regarding the reloading speed issue, there are a couple different magwells that are available now. These are bolt-on parts that may or may not require grinding the mags a bit. Once done the reload speed and ease of locking in a new mag, even with the bolt closed, is amazingly fast. Of course you do have to have extra mags available but I believe that the point of a mag feed firearm of any sort is based on having extra mags available, and not to reload a single, empty mag.
If one can accept that basic convention, and you try it, you'll never want to use a tube fed shotgun ever again.