That would work as a secondary regulator, which is what it's designed for. In that case, your inlet pressure would be well below 300 psi, so it should work fine. Unless it breaks randomly like crane mentioned. This isn't designed to be used as a primary regulator, and it never should be.
It doesn't include any fittings or a gauge, so it's not the biggest bargain in the world. Say you spend $5-10 for a gauge, maybe $10 on all the fittings (inlet nipple, outlet ball valve, check valve, outlet barb, etc.) and you're looking at $25-30. You can get a solid Tapright setup for about $50, and you'd never have to worry about it.