I have one. Mine is the 10 inch barrel. I have cylinders for both the 450 marlin and the 45-70 for it.
If you hand load you can get pretty much any kind of power you want from it. I have loaded some 300 grain bullets down to about 600FPS and the recoil is very small. I have also loaded some 325 grain bullets up to 1800 FPS. I also have shot some 500 grain bullets at about 900 FPS.
If you already have a large hunting revolver I would get some thing else. If you dont then the 45-70 is a fine choice. If you hand load (I highly recommend it) the 45-70 is in the same league as the 450 marlin. If you shoot factory ammo the gun will be very pleasant to shoot.
Shot placement is everything! I would rather take a round of 50BMG to the foot than a 22short to the base of the skull.
all 25 of my guns are 45/70 govt, 357 mag, 22 or 12 ga... I believe in keeping it simple