Having had it only for a day I still felt impelled to pass along some things I learned from using this pump.I've been using the Dolphin hand pump for a while now and it works well but my complaint is that when the bottle is full it works great since it works by compressing the air space inside the bottle to push the water up the pipe and all the compressed air comes out once you stop pumping. The problem with that is when the bottle gets emptier and emptier you have to pump several times before it starts to come out since there's more space to fill with air.Here comes the pump to the rescue! I put in four Eneloop rechargeable batteries I've had sitting around for a couple of weeks with the D cell adapter that takes two AA each. It works perfectly fine with these batteries and filled my 32oz bottle pretty quickly. In fact I forgot that you press the button once to turn on then you can lift your hand off but I held it down. When I lifted my hand it kept pumping! Oh yeah, press the button again to turn off. Remember that!I have the Hinkley and Schmidt 5gal bottles and found it actually sits on the lid but if you press the loose plastic outer ring down then turn clockwise it tightens down so it is firmly attached to the bottle. It's no air tight seal like the Dolphin but there's no chance that thing is coming off. I'm not sure if other reviewers just couldn't figure it out or not since if this didn't fit snugly the Dolphin one probably wouldn't have either. It fits just fine.The bottom of the pipe sits lower than my Dolphin as well.Yes the water speed isn't as fast as the Dolphin when the hand pump is in a full bottle. However if your bottle is only 1/3 full this pump will be pumping water out easily while you're still pumping away to get that pressure built up inside. I think I'm preferring this pump.Some people say the motor is too loud but I found it only slightly louder than the sound of me pumping the hand pump and sometimes quieter since the hand pump sometimes makes squealing noises if you press down at a slight angle. I call them a tie.Overall I'm very pleased with this pump so far and I'm shocked at the price. I'll update this if it lasts only as long as how cheap it is but I'll be positive for now.Update Dec 21, 2013: I'm still on the same set of batteries after maybe 8 5 gal bottles. I forgot to keep track. However the odd thing is it doesn't sit the same in every bottle. One time the pump wasn't pumping so I poured the remaining into a 32oz bottle and there were 30oz left. One time it stopped pumping and I poured out the water and only 8oz was left although most of time it seems to be around this area. Perhaps I didn't seat it down enough when it resulted in 30oz left. This last bottle I couldn't get it to seat down firmly like the others and I see that the bottom of the tube is pressing against the bottom of the bottle. Kind of erratic. However it's still pumping water very well and quickly on the same set of batteries so I'm impressed. Again, I'm not even using D cell batteries, just two sets of 2 AA Eneloop batteries in an adapter.Update Jan 31, 2014: I'm still on the same batteries! I've been expecting it go die out for a while now but it's still pumping pretty fast. In fact with my 5 gal bottle about 3/4 empty it only takes 22 seconds to fill a 32oz bottle.