I have a 980 Ti Hydro Copper. No idea on restrictiveness compared to other blocks as I have nothing to compare it to. They are likely specifically made for the Hydro Copper application. However, them being different doesn't mean "bad".
All I can really say is that the block works really well to cool the GPU. Even at the highest over-voltage allowed by the stock BIOS and highest overclock, the temp has never gone above 50°C. And it's in the same loop as my overclocked 6600K. I do have to admit that I have two 360 radiators cooling just the CPU and GPU, so that's likely a big influence.
Edit: Based on my experience with this one, I'll be looking at EVGA graphics cards in general and Hydro Copper cards in particular for my future purchases.