Most AIO pumps are either Asetek or under the Asetek patent. Their patent seems to cover everything but the water, but that debate is old and separate from this. There are a few that use their own design (Alphacool Eisbaer is one) The weak point of AIOs in general is flow rate, due to pump limitations. The standard D5 type pump plus waterblock would have been too heavy, bulky, and expensive. To be marketed as an alternative to air coolers they couldn't be priced at $200+. AIOs weren't introduced with the intention of being the last word in cooling. They were introduced because all the cool kids had custom liquid cooling, so it was thought they could sell maintenance free, easy to install, closed loop coolers by the truckload. They were right. It's really only been a fairly recent occurrence that high level cooling performance has started to be "a thing".
The reviews of the various AIO solutions (and there are a lot of them) generally come to the same conclusion, with few exceptions: They match high end air coolers, some slightly better. To beat the best air coolers you'll have to spend more, a lot more in the case of the really good ones. I'm happy with mine, it handles the highest temps my CPU puts out (mostly), but a small custom loop would likely knock 10-20 degrees Celsius off my peak temps stress testing. The Alphacool Eisbaer I mentioned seems to do a good job, and it's expandable. That might be worth checking out, too.
