I did a little test and printed a paper copy and cut them out. I may not have done it correctly but, I was not able to get the front and back of the "decals" to actually line up, regardless of how I oriented the two sides of either set of decals. There is a significant difference in size of the front and back decals. My test may not be entirely indicative of the actual final result because I didn't have a 3D propeller to try to apply these paper cut-outs to. However, my test suggests that from the front, the propeller will look good, just as in the vendors listing, but viewed from the side and the back the laminated wood doesn't seem to match up completely for either propeller. Clearly the larger front decal will have to wrap around to the back of the propeller but from my test it didn't really look like it would be a perfect alignment. Also, the instructions indicate to trim or sand the excess away but I didn't see a way that front and back face would line up in either case. I think some hand painting touchup will most likely be required along the propeller blade edge or wherever there is an interface between the front decal and the back decal.
I did a Google search and was unable to find a review of the product to hear from someone who actually had the decal and tested it.
Some folks may not even notice. I have to admit from the front, which is how most of us would view an a/c displayed, it should look very good indeed.
A better test will be to actually purchase a test subject and apply the decals to the actual intended propeller it is difficult to judge if there would be an improvement or how effective touching up the edges where the two decals will meet will prove to be. Perhaps someone on the forum has already purchased this product and can relate their experience.
It may be possible to fabricate ones own propeller decals for other propellers for other models but with perhaps better control of the edges/interface between front and back decal. My thinking is to take the actual kit propeller and create a template of it and then remaster the decal artwork to ensure the edges will line up more closely - without significant overlap or trimming. in this same way, the amount of touchup may be reduced and an even better looking propeller is possible. Testing is required.
In my case, I want to explore feasibility for 1/48 scale. It may be more difficult to produce a nice result at that scale.