Would you recommend those pre-assembled/ AIO liquid coolers?
Short answer is no, I do not recommend but a very few of the pre-assembled and filled systems. I do like be quiet! Silent Loop. I have a 280mm one and it is the only AIO I have used over the years testing and reviewing that I have kept in a system for longer than it took to test them.
Long answer requires a quick tutorial of what AIO's and CLC's are;
CLC's are a sub-group of AIOs. Most of the AIO's sold are CLC's, like all Corsiar, NZXT, EVGA, Themrmaltake, Arctic, etc. are almost all made by Asetek with a few made by Apaltek, CoolIT and ID-Cooling. All CLCs have aluminum radiators and no provision to add coolant or to change / replace components.
Asetek are almost identical pump/waterblock and raidator with differnt fans and different cosmetic looks and brand labels. Asetek does not publish pump flow rate but independent testing shows them to be 40-61 L/h. Enermax Liqtech TR4 pump is rated 450 L/h and ID-Cooling Frostflow is rated 96 L/h.
AIO's like be quiet! Silent Loop, Fractal Design Kelvin and Alphacool Eisbear are made by Aphacool and while using same radiator use slightly different pumps rated 72-100L/h. Swiftech H series AIOs pump is rated 660 L/h.
All of the above AIO's not CLC's have proper threaded fittings, fill port, copper radiators, .. in other words much better build the CLC's ..
But still not as good as most custom loops. The most popular custom loop pump is EK-D5 with a maximum flow rate of 1500 L/h. Most users run pump at 1/3 to 1/2 speed, so flow rate is much lower in normal use, but still many times higher then CLC's .. and even though AIO's that are not CLC's have significantly higher flow rate then CLC's, only Swiftech and Enermax Liqtech TR4 are anywhere close to custom loop pumps.
I did not like CLC's when they came out and was very out-spoken about their shortcomings. In the years sense I've seen many CLC owners come back to top tier air cooling .. and even some dedicated custom loop people are coming back to air cooling. Reasons are many but mostly cost and maintenance.
As orbitalwalsh posted Silent Loop 280mm is £139.99.
Dark Rock Advanced is a good upper mid-level cooler. It is quiet at the loss of some cooling ability. be quiet! make some of the best looking coolers, along with Cryorig.