None of the Bell 47's I've ever flown had a key-type mag switch. They all had that old design that was probably invented for airplanes in the 1930's. I'd imagine that as those old switches bite the dust, people replace them with modern key-type switches.
No turbine helicopter I've ever flown needed a key. Nor do airliners, turboprop airplanes or business jets need an ignition key.