The Faber-Castell nibs are great. BTW, you can put the nibs from the Loom into the TWSBI Go. No more issues with the grip then. 
Interestingly it’s too loose for the Eco.
The Hexo nib however looks more like the nib of the Grip, which is a bit different, but also great. And that one then fits into the Eco (but not the Go).