I actually own a Magneet; model "sprint". Because I actually have one, I know a bit about the company. The original company produced bicycles until 1969, where-upon the Magneet company was bought out by the larger Dutch manufacturer Batavus, the spelling of which I believe I have just mangled badly. Batavus produced bikes under the Magneet name until about 1972.

Most of the Magneets were city bikes.

I bought mine at an auction for a fiver, attracted by the odd nameplate, the Campagnolo mechs and shifters, the wild seat, and the very cool old wignuts for the hubs. It's too small for me; if it were my size I'd have built it up by now into a fixie or something. Nothing special, although the paint is very good. I think mine dates from the Batavus (?) period, because the Campy Gran Turismo derailleurs weren't made until 1970, near as I can figure (they might be later upgrades; but the GTs are very low end Campy, so it is possible they were stock). It has "racer" brakes (a Mafac knock off, I believe), cottered cranks, the same lugs and paint scheme as yours. Steel rims. Somewhere on-line there are some Magneet brochures from far earlier than either of our bikes; I looked and couldn't find them again, but I gave a fairly cursory google search.

What I've been able to find suggests the bike was threaded French, though I have yet to take mine apart and actually find out. I'd have built it into a fixie for someone else, but it's a cool frame, so I may build it up for my next girlfriend or something.