You're much better off with a 'pea shooter' style of flowmeter which has a ball that rises showing the gas flow, far better than the dial type fitted to some regulators.
No don't use a peashooter. You'll just waste gas and could then run out.
I have one, but I'm not a lover of peashooters for MIG especially. A rough ended shroud combined with an unsealed
thread or slide on spring at the base of the shroud doesn't lend itself to accurate metering IMHO.
I was meaning more for at the regulator itself. I know you can get the ones that go at the torch and I'm sure they're useful at times, but for everyday work on a set that doesn't have leaks I'd always choose a peashooter at the regulator!