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.received the item in perfect condition with the assembly instructions within the expected time frame. I installed the unit to a 5-gallon drinking water standard plastic (boa free) bottle with a thread less opening at the neck. Simply insert the unit in the opening as it fits perfectly then turn the outer ring to the right until you see the close/open mark. You will it locking in place. it closes to a perfect water tight seal. Install a couple 2 new D batteries unscrew in the battery compartment on top of the unit. The materials look and feel top of the line, in fact, they are Food Grade, which means they will not degrade the drinking water and safe to drink. Before installation do not forget to pour your water at least 1/3 full. After the installation i pressed the blue button at the top, you can hear the motor of the pump working and pumping out a constant beam of water through the nozzle. I actually timed the rate of water flow coming out into an empty bucket. 3 litters per minute with brand new batteries, as the manufacturer claims. Very happy with this purchase so far. do not know how long the battery will last, I intent to use it for camping, sports.Overall I like this. The battery life is good, and it does a good job. Beats spending far more on a ceramic or somesuch to hold the bottle upside down.Now for the down sides:1) Tube goes STRAIGHT down, and my bottles have a rise in the center of the bottom, so there's still about 1/2 a gallon or so of water in the bottom each time.2) This isn't going to cinch up well on other bottle designs. In fact, when we tried other company's bottles, it wouldn't hold at all.3) Can be a bit messy. Make sure to leave the neck unfilled so the tube can go in without overflowing.4) Need to clean the tube off from time to time, but need to bear in mind that you're putting tap water into your clean water, OR rinse that tube with some of that water, if purity is a big issue for you (as it is for us).I'm probably going to add a bit more flexible tubing to the end so it can get more of the water out of the bottom. Meanwhile, a funnel and a spare 1 gallon jug come in handy so you're not wasting the water you bought.This little gadget has really made camping so much easier, thus fun. We refill the large blue water bottles at home and bring them with us. The tops are gone so we simply cover with plastic wrap and a rubber band. This keeps water from splashing out during transit.When we need to get water we can just set this pump in attach the spout and push the button. This sure beats trying to lift the water bottles to pour into a dishpan!I would give it five stars but it doesn't attach to the top of the bottle, it tips around a bit. Or I can't seem how to get it to attach. Either way, it doesn't. But more importantly it gets the water out nicely! One of my better buys.REVIEW EDIT, 9/26/14. I have now used this pump over a month now, on and off. I have found that leaving the batteries in while not in use for awhile, several days to over a week cause some light corrosion in the battery slot. The pump didn't work until I was able to clean up the spring that secures the batteries. I now remove them when not in use for a day or more. I still like the product.