eal-fill will just be an aluminium coloured filament.
It's good if you want something that's does look really metallic. But not so much if your think it's going to be stronger because it's got metal in it.
It's not :-)

As fars a s the nylon 645 went.
Yes it prints easily, yes there's great layer adhesion and no discernible warpeage - but it doesn'ty stick to printbite.
Probably the cleanest print I've yet had from nylon.
So as far as I could tell from the limited print I got before it unstuck itself - it really is as good as they claim :-)