Things I liked:Makes filling even more convenient, no more messing around with silicone grease! This allows you to make all your air rifles use a common fill fitting, which is a HUGE plus! Things I would have changed:This was machined flat on the bottom, however the fill port on my Sumatra went into a cone shaped depression. This made the stock o-ring NOT work, and you'll have to get a thicker o-ring or washer to get an air-tight seal or it WILL leak. PYRAMID NEEDS TO ADDRESS THIS! It's an unfortunate lapse on what is a great product otherwise. What others should know:If you bought one of these and it leaks, just get a fatter o-ring for it. Also, make sure you get a filler cap to keep dirt out of it when you're hunting. This is a great way to make multiple air rifles all compatible with the same fill setup. I'd give it 5 stars if not for the o-ring situation! According to Pyramid's tech support they were able to use a .105" thickness o-ring to fix the situation and are sending me out a couple, but I couldn't wait and found one at the hardware store, works like a champ!