I'm just testing out Windows 10 now. I installed the 15.9 drivers, then used the 14.4 mobility driver to install the HydraVision package. HydraGrid is working well except for one small (use case) scenario. I use ObjectDock and remove the Windows TaskBar which I find much better on three monitors. On Windows 7, HydraGrid would snap windows in the lower quadrants all the way to the bottom of the display, but in Windows 10 it leaves a gap where the taskbar used to be. As well, there is a small gap between windows now, where Microsoft has clearly trimmed the fat on their windows.
Would love to say this could be fixed... but I don't think Hyrdavision has been touched since ATI was bought by AMD.
Might have to resume the search for window management software (but it all hates eyefinity)