I would definitely want to see the list of directories before I decide to buy it. I anticipate this is probably part of your moat and you may not wish to share it just like that (although if you do, I personally think it would be good for your business, but w/e).
But ... that's not the real issue, though, the fundamental issue would be me regretting getting this because after the paywall it turns out that only 2-3 out of the 150 are worth it and the rest are kind of low-quality. Minimize that perceived risk and I'm sold 100% (and I guess others' too).
I want to emphasize this is not a negative comment, I really do think this is a great service to have at hand!
yes it depends mostly on the directories you select and the ones that accept you but I've tried with one of my startup and I gained around 100 backlinks in a week.
In term of Domain authority, I was starting from very low but I also saw some changes even it takes a few weeks to being updated.