I'm to scared to have it installed because you know how that stuff works - when your the first ones to install it you experience all the issues. I will wait a week or so until I know all the bugs are worked out. I'll sleep better haha.

I've updated and the new features are ok but really I was hoping for more going from 3.x to 4.x The code has been re-worked a lot though apparently

What were you hoping for? There's quite a bit you can do with WHMCS..

TBH I don't know what I wanted new, maybe im being unfair there, oh my one negative of it is the new default backend is worse than before, luckily you can revert

the stable version of V4 is out. I am going to upgrade my whmcs soon.

How much it costs a license to use this script?

v4 is ok. I've been using v4.0.2 for a little over 2 weeks now -- stable. I think they re-work abit on the codes too. Not too sure on that.

It's for $13 ~ $18 a month (leased).
I'm on 4.0.2.. so far so good. working stable

Using 4.0.2 here...rock solid and great.

Running 4.1 myself. I recommend it. Upgrade was simple, new features are nice, and a little more clean of a look. Seen 0 problems in the last 2 weeks.