Despite what is said above, you as a consumer have zero ability to determine what is or is not good leather. Full stop. The only determining factor is a products' history and as stated, Schott and Cockpit USA have a great history of quality. But, sadly, that reputation could turn on a dime.

What to know the real skinny on leather from people that know better than random asshats online? https://nstarleather.wordpress.com/2018/05/31/the-grades-of-leather-hierarchy-youve-probably-read-about-is-a-myth/

The jacket you linked to will probably do just fine. I've looked at leather stuff my whole life and not once ever heard lambskin referred to by any other terms than "lambskin" and never heard qualifiers like top grain, full grain, etc. applied to it. If you like and can afford it, get it. Is it BIFL? Not really as lambskin is naturally a sucky leather in terms of durability but this jacket is obviously a fashion jacket in a suitable leather type and I doubt you'll be wearing this on top of a utility pole.