I would want to know how thick the leather is in this kit. Most folks suggest and use 3-4 oz. thick leather in cowhide. Heavier leather is just heavier, it does not add much to the pouch except it is a little stiffer to get in and out of it, if you like and want that. (I have a couple heavy pouches and like them, but not everyone does.) Oil tanned leather often goes at 5-5 1/2 oz. so it is not hugely thicker/heavier than what a lot of folks use.
However, though they had oil tanned leather in the 18th and early 19th centuries, modern oil tanned leather is not a period correct tanning technique, if that matters to you for authenticity. (Vegetable/bark tanned leather is period correct for authenticity and is commonly available, though normally higher priced leather.) Modern Oil tanned leather can be a bit harder to hand sew as the oil makes steel needles slippery. That doesn't mean you can't hand sew it though, it is just not as easy as Veg/Bark tanned leather.
Madison Grant reports that most shooting pouches were made from cowhide or pigskin and of course deer or elk skin depending on when, where and who made it. He also reports that earlier 18th century pouches had a tendency to be square or rectangular. The "D" shape pouch, which this kit appears to be, is very late 18th century at the earliest.
There are reported to only be only about 10 shooting pouches that can be documented to the 18th century. These pouches are a bit smaller to a good bit smaller, when one includes the original Lyman Belt Pouch, than what the leather is in the kit. So you could take this leather and make it into a smaller bag, if you wished for an earlier period pouch.
So if strict authenticity is not on your requirements list, this kit is pretty inexpensive and you could make almost any style pouch you wanted from it by custom cutting the leather to what you want.
Gus