Never had to deal with JNC how are they compared to comikey (the bane of my existence)
I'm a JNC member, so I'm a little biased, but I think they're decent.
Their subscription service is basically $5 per month to read any currently translated chapters of series (so for Bookworm, you can't read early volumes unless you buy them directly, but you
can read any current chapters before they're compiled into volume form). They also offer a "catch up" service, where every month they make a couple series fully readable - so for example, this month
Doll-Kara was the catch up, so until the month ended you could read all six currently-translated volumes.
Their coin service is definitely more transparent than other services. One coin equates to $0.01, LN volumes are usually 699 coins and manga volumes 899 coins. The coin system is a bit obtuse, but members get a discount when purchasing extra coins. And, most importantly, any series you purchase are released DRM-free - so you can read them whenever you want without someone taking it from you.
There's a couple of things that I would like them to improve on - they only work on the manga when they get the rights for the volume version, so simulpublishing will never really happen, and I'd like to see more readable things for a member outside of current releases and catchups - but if you want to support the official release, it's one of the better options out there.