I've no experience with the Darkbase case, but i've got the A240g so I can share my experiences with that
It's a great kit which I picked up cheap and its the most fun i've ever had building a pc. The downside it was a gateway drug to make my expensive hobby even more expensive
It generally performs well and keeps my overclocked 8700k and 1080ti under fairly good temperatures, but i've noticed under certain heavy gaming it can start to struggle. The gpu can get to 60+ degrees when both the cpu and gpu are getting hammered, Cpu hovers around 65c-70c ish. The air blasting out of the rad feels warm, the tubes feel warm and the water temp reached 48c with an ambient temperature of 24c.
I feel the 240mm rad isn't enough for two overclocked components being pushed hard, unfortunately no one sells the expansion kits in Norway so I'd have to import it direct from EK, which bumps up the price to something i'm not comfortable with.
I've ordered an aluminium radiator from elsewhere, its not EK made but hopefully it will work fine, I'll report back once I've got it if your interested on how its effected my temperatures
So to sum up, its a great kit but it will struggle to keep things super cool when overclocked/pushed hard.
I've seen copper kits sell for roughly the same price, minus the gpu block. If you can push the extra cash and go for a copper starter kit id recommend it. It gives you more options later down the road when you want to expand the loop or add flow meters, drainage ports etc or if EK decide not to release a new GPU block for newer cards.
If your on a strict budget or get the aluminium kit at a good price then its a good starter but you will need to expand it with extra rad later imho