I'm not too technical, but I've been using Calyx as a daily driver for more than a year, and I'm pretty happy with it. Works more or less like any other phone, just can't use banking apps.

I think I ended up using Calyx over Graphene because I heard it was more user friendly, and maybe also compatible with a wider range of apps.

I've not used Grapheme, so I can't really say anything factual about the comparison.