Mine was easy enough to set up, sure... but it's not something most of my gaming friends would be confident doing themselves.
Even so, it was nerve-wracking as heck getting the GPU blocks on. I've had to help a friend do his because, despite being a long-time experienced builder and overclocker, the possibility of knackering £2000 worth of graphics cards was making his hands shake!!
My loop also cost me about £400 in all, whereas a pair of decent AIOs would have been less than half that... and even less in the sales!
The best part of AIOs is the plug & play aspect.
Having two separate AIOs for CPU/GU means you can swap one out without having to drain and re-jig your loops. It also means you don't have to buy expensive blocks every time you upgrade.
I'd never go back now I'm properly w/d'ed, but as a simple solution and for the money, my AIO was great!