No, it'll be better than a chinese one. Even in the 70's detectors were air testing on coins at the same distances as modern detectors. The let down on older machines in recovery speed and ground balance abilities.
Recovery speed is how fast the electronics can recover from the detection of a metal item. It has the biggest effect when you have a iron object next to a good object. The detector gets the iron object and discriminates it and then before it has reset itself you have already passed the coin. Just run it a lot slower than you think you should.