I am using up about 400gb of my 500gb 960 Evo and thinking about getting an additional 970 Evo to add in additionally. I'm new to M.2 still as of this build about two years ago. Can I simply clip in a second M.2? It appears there is room for a second. Any issue with running two of them at the same time? Any issue if one is a 960 evo 500gb and the other is a 970 evo 1tb? Trying to troubleshoot before making a purchase of a new 1tb 970 evo I guess. 
Thanks.

Thanks.