It's been almost a month since I last posted so here's another update!
Niko is doing well. Super tame now. As soon as I go anywhere near the cage he'll come up to the door. As soon as my hand goes in the cage he hops right on a waits to come out. He's not skittish at all now (except when I move too fast). When I hold him he's very relaxed and doesn't seem to want to escape.
He no longer goes in his ball, he free roams. Again, he's very calm, very trusting. He'll climb all over me, sit on my shoulder. He'll come when called and will allow anyone to handle him.
Unfortunately, the bin cage broke so I have got him a wire cage with the floor space being 486² inches of space. I've taken all plastic out, except the wheel so now it replicates his natural environment somewhat.