As someone who owns both of these (and many others) I'd personally recommend the Nyth all day and all night over the scimitar.
The Scimitar (much to my chagrin) has never reliably worked. Mechanically it's a great mouse, but has been plagued with issues since day one. The random side buttons failing to respond and often requiring the cord to be pulled out the USB port and back in or worse, rebooting really has never been fixed. Not sure whether it's any better with CUE 2 but the Corsair forums are full of complaints about this mouse. Also just thought, mine is not the new "pro" version but the original, not sure which version your considering.
The Nyth on the other hand has hardly given me a moments trouble and being modular is great to set up how you'd like. I play a lot of WoW and use mine for raiding and as my daily driver. It's very comfortable to use for long periods but ymmv. Just be aware that the 3D printed buttons you can get for it from Shapeways are awful and look really crappy compared to the original buttons. This is however I believe a limitation of 3D printing. Using mine on a slamepad and it tracks like a champ and the feet are still going strong despite all the use it sees.
Best
Wulf