How effective would this be or would the Earth's magnetic field make it useless? Would it take too long for this to be of any use?
Scoping is an interesting idea if you can fuse hydrogen as fuel as you go along, but not so much if you just want to tank it.
Setting aside how the scoop itself works, there’s a problem scooping up stationary gas: you have to bring it up to your speed if you want to put it in a tank and keep it there.
Essentially, you need a way to take your newly acquired fuel up to your orbital speed. That takes most of the energy and $\Delta v$ it would have taken to lift it from the ground; you save only the gravitational potential, which isn’t a large fraction if you’re close enough to Earth to catch something.