You don't need to be a pro, just be able to afford them, but it's actually quite quick to get to that standard.

I've had a similar file set to of those three Amazon nut files in the past and whilst they are certainly better than no nut files, on mine the width wasn't well regulated. Certainly on my set the high E slot created was just as wide as the G slot. When I got my Hosco set, I replaced the nuts on the guitars I'd used those files on and I was certainly a lot happier with the end results.

I'm also not that keen on double-sided style files in general, due to the V-shaped notches they make (even though Hosco do a set that is far from cheap). When string bending your strings are more likely to pop out of the slots with angled sides if you don't have relatively deep slots. If you like to have about half the string poking above the top of the nut, you really need straight-sided nut slots.

But I do wish that a good set of files was a lot cheaper.