The 9A5N isn't exactly new. Following is an article I posted in 2015 about the 9A5N key:
https://www.eham.net/article/34318. (It even contains pictures.)
It is still the only key I use, except for QRP out and about, then I pack my Begali Magnetic Traveler.
In the past, it has taken time to become accustomed to a new key. With the 9A5N I 'got with the program' virtually immediately. I did the sensitivity adjustment about 3 times during the first few months and it has been years since I've performed an adjustment. I use Lithium Batteries (not the rechargeable type) and replacement has been at such infrequent intervals I don't even remember how often they've been replaced. Of course, at my age there are quite a few things I don't remember, or maybe it's that I only remember the important things now.
Emil
W9NM