Crawl spaces are .... considered as 'damp,' and the common / near universal practice of running NM through them is a code violation. Thank the latest version of the NEC for making that clear - as well as some very active politicing by the home inspector lobby. I report, you decide ....
As for "Relock" .... Relock is a brand name of a pre-assembled system of MC and snap-together connectors. I have only seen it used with lights, and I do not know if it is made in a more versatile form. As a listed system, it typically has several circuits in the cable, circuit distribution is determined by the connectors used, and wire sizes can change between sections.
It's not really possible to know the wire sizes within the cable, so you have to pay particular attention to following the directions.
It's the directions that would determine whether the product can be used in a crawl space, or for any particular purpose. The Relock assemblies I have used appeared to be similar in construction to the 'dry location only' MC fittings. It is possible that there are other products on the market.