I have the 15lb. Northern Tool stuffer and am glad I got that instead of the 5lb. You buy one butt it's going to go 6-8 lbs. average so with the 5lb. you know you're going to have to reload it twice. With the 15 lb. you can do it in one shot.
I bought a two-pack of butts Fri. and made Italian sausage today, it was 14.5 lbs. I couldn't get the whole amount into the stuffer so I had to reload once, but I did about 12lbs. in one load. Had I had the 5 lb stuffer I would have had to do it probably 4 times to get it all done; that's too much work for the price difference. Plus, the 15lb. does have metal gears and built like a tank, all stainless steel and super well built. I don't regret the purchase whatsoever.
An 11 lb. horizontal stuffer again is less capacity and being horizontal, it's almost required to use two people to stuff - one to crank and the other to feed the casing - the spread between the two operations is too far to reach by one person. Hence that's why they came up with the vertical. I would strongly recommend the 15 lb. 'er if you can see your way clear in spending that much, you won't regret the investment, and if you don't you'll be always asking yourself "I shudda.." Your sausage making will increase as friends and family become super impressed by your talents and you'll definitely need the extra capacity. I'm now thinking by retirement I may need to upgrade to a 30 or 40 lb. capacity one!