Reliability has been 100% so far. HS recommended high-base/Magnum rounds but mine has cycled with regular and even Federal LE132-00 reduced recoil buck and the Fiocchi plated rr buck.
You can't get an extended magazine tube from anywhere, so if you want one you must have it made.
1) Get an extra magazine tube from EGunparts or elsewhere.
2) Have a competent gunsmith put it together with the old tube so that is is a minimum of 18 and preferably 18.5 long. Best bet is to measure how long 4(?) shotshells are and compare that with the length of the standard tube, then measure 7 of your preferred shells and leave enough room for spring compression. I mention this because I've found Federal LE132-00 to be just a bit >.< longer than the standard 2.75 inch shell and it adds up after a half dozen are inserted.
3) Use a lathe and have a custom-turned cap made to hold the two halves of the receiver together. It's not a complicated part, all it Really needs is a 45-degree bevel on the inside.
4) Fit, measure, and scribe a line on the tube with the new cap holding the halves together and the magazine tube backed out a full turn or so (to provide clamping force when it's all together)
5) Fasten the new cap to the custom made extended tube and you're pretty much done.
... 6) be sure that the new, extended tube has holes laterally through it like the original tube did. You can use a screwdriver or cleaning rod to provide a turning force on the tube to screw it tight or loosen it.
You can also have the stock rear sight tower removed and a Picatinney rail put in place, the height of my red-dot is almost exactly where the original sight was. (I found out that a clamp on M4 sight is just a bit too high for the stock front sight but it could be replaced with a taller one that could even be fixed in place if desired.
I would personally just remove the front sight and have a custom made door standoff or compensator silver soldered in place as the front sight needs to be removed every time you are going to remove the upper receiver cover for cleaning. (I rarely remove mine now days.)