Yeah, it does a decent job as a cleaner, lubricant, and as a protectant but dedicated solvents, lubricating oils, and preservative oils do a better job at their intended task.
It will likely work just fine.
I never cared for tamales very much for the longest time. I mean I liked the flavor but I always thought they were tough. Then one day someone laughed at me for eating the corn husk.
Is there anyone how puts a thick coating of grease on their flintlock or percussion lock? I would think it would work fine as well but having all that grease up against the stock would be problematic.
If the barrel says great plains rifle it is slow twist. IF it says great plains hunter it is fast twist.
Investarms barrels that are the same except for their markings are still available from Track of the Wolf and muzzle-loaders.com but may or may not be in stock at any given time.
Track has a .54 in stock. Says 1-60 but I thought those should be 1-48.
https://www.trackofthewolf.com/Categories/PartDetail.aspx/647/1/BBL-54-C-INV-28-B
I don't see a problem with it if it is the best tool for the job that you have available as long as it is legal and done safely.
A 44 ball is probably a better performer than say a modern .380. My biggest worry would be for the potential for cap jams. Obviously the size of these guns are not...
Although I am sure reloading from a pocket or pouch in the real would be slower that reload was quite impressive. There are not may out there that have become that proficient.