I took a look at the Tried & True web site; their FAQ indicates their finish is intended for wood but can be used on metal surfaces, as well as others. It is a polymerized linseed oil material, like many or most oil-based varnishes. Other similar products likewise indicate compatibility with metal. Of course, metal will not absorb the oil so apply sparingly.
In other words; there's no harm in trying it. And, once you've tried it, you can let us know if it's...Tried and, um...True.