I've been doing some more searching, (still can't find the article I was looking for), but I do agree with several articles I ran across as I searched Google...
Geometry of the, cock & frizzen, hardness of the frizzen, pitted frizzen -vs- smooth, flint placement in the jaws,,, it all plays together,,, and all I read actually had positive things to say about the French Amber Flints... There was one mention of the fact that the only draw back is that it's a one-side flint and can't be turned around like the English Flints... However, from what I also read, several were saying 40 to 60 to 80 to 100 shots from this single edge style French Amber Flint...
Again, I agree with John, if the price is right - why not give them a try.