The H240x is however not a custom loop, that would be a contradiction in itself. Something prebuilt that is the same for every buyer can't be custom. A custom loop is what results if you buy a pump, tubes, lubricant, fans, possibly peltiers, etc yourself and put them together to work as one system - a loop you built yourself. The H240 is nothing like that, it's an All in One water cooler like the H100i/H110, just that it's quieter, cools better and that you can add additional parts later on.
Also, cleaning dust out? That's what you'd do with an air cooler. You barely need to do that with water coolers as the only parts that can accommodate dust are the fans. What you will need to do though is refilling lubricant (vaporization is real), clean the tubes and possibly tighten screws once in a while as water coolers usually rely on high pressure You won't need to do that often - maybe once in two years, but you wouldn't have to do it more with a custom loop either.