Things to look for based on my experience with the A240G kit:
1- Read the manual and instruction even before buying this kit (https://www.ekfluidgaming.com/EK-IM/EK-IM-3831109890721.pdf) to get familiar with the process
2- Review the videos provided by EKWB before buying the kit (https://www.youtube.com/user/EKWBofficial/playlists) to get even more familiar with the process
3- Figure out the position for the pump/reservoir combo first
=> The combo can be mounted on a bracket which then connects where you would have a 120mm FAN. For me the only place was behind the PSU and I needed access to the bottom of the case to screw it in (which had a cover). so make sure that you have a location in mind for the combo prior to setting this all. In my case, I had just enough space between the PSU and combo for the cable to passthrough but it might not be the same for you.
4- Make sure you have enough room for the reservoir as well and make sure you have enough airflow in your case
5- Do not over tight the fittings. EKWB provide an HEX KEY to be used and I recommend tightening all the fittings with it but make sure not to over tight then as you will damage the thread and leaks will occur
 
Things that went wrong:
1- Defective CPU backplate in my case. One of the thread on the backplate was damaged upon arrival and I could not tight it up from that side. I had to purchase a new backplate on Newegg as EKWB was closed 2 days for a holiday and I was very impatient. 
 
 
So far this was a pretty easy and I would totally recommend doing this for those who can't afford a fully custom loop (which would cost 2x - 3x what this kit cost) or for those whose like me wants to get started but do not with to use an AIO as I will (for my next build) definitely go with a custom loop.
As far as temps, I can't give you a before and after for the GPU because I installed the waterblock on the GPU as soon as it arrived but my old 1080 would get to the 70s and the 1080Ti (overclocked to +100Mhz which gets to a max of 2062) stays in the high 40s and sometime low 50s. My CPU which runs at 4.6Ghz gets in the 60s to mid 70s depending on the load.
 
I hope this was helpful to some,

I watched this video from JayzTwoCents and he got some good results. I think he even had the 240 rad too. The cost is also attractive considering the performance is on par with copper, my only concern is the option to expand. It seems the only company crazy enough to use aluminium for waterloops is EK and they have a rather small selection at that. I checked the 360mm "Alustream" rad and it's not in stock, so even EK don't have them lol. In any case *ahem*, nice looking loop you have there. 
 
 

Valtrius Malleus
I watched this video from JayzTwoCents and he got some good results. I think he even had the 240 rad too. The cost is also attractive considering the performance is on par with copper, my only concern is the option to expand. It seems the only company crazy enough to use aluminium for waterloops is EK and they have a rather small selection at that. I checked the 360mm "Alustream" rad and it's not in stock, so even EK don't have them lol. In any case *ahem*, nice looking loop you have there. 

 
I do believe that EK has planned in extending the fluid gaming line (which the A240G) is part of but I am not exactly sure what is to come. I would not be surprised though if we start seeing fittings, bigger radiator, etc. coming out in the next few months.
Price wise, you could technically buy 2x of those kits and use one for your CPU and one for your GPU and still pay less that you would for a full custom loop but then you would have 2 pumps or you could replace it with a larger one?