Thank you for posting these--anything Newfoundland gets my attention.
I have seen this now and again, and while I have never met a Newfie item that didnt open my wallet, I've never bought one.
They are not official stamps of course and evocative of the 1910 John Guy stamps in general--though they date from around 1900.
They are not in Unitrade, but I believe in Walsh/Butts the "NSSC", they are referenced as bogus items. It was not uncommon back then for private companies to create stamps.
Sometimes they "break the ice" and get some sort of recognition among collectors or quasi-officially. These are not mentioned in Boggs seminal history book, I believe (but will check tonight). They are referenced by Walsh/Butts who writes that he is "often asked" about them (so I wouldnt bother contacting them).
More specifically, they are referenced with a photo on page 140 on the NSSC, and described as "Paris Essays"; grouped there with some other bogus stamps by Roessler (an air mail stamp, which I do have), and some Labrador labels (I also have these--only because they were throw-ins for a collection I bought).
If I were you, I would keep them if you like Newfoundland. If not, sell them or trade them--either on
ebay or I might be interested. Hard to say what they are worth, but safe to say not a lot.