Despite the fact that support from LPanels coders is lacking at best, the software itself is actuaqlly extremely nice. We switched to it after ModernBill started failing nearly all credit card transactions for no reason that I or the support techs could figure out. I have to say, I like the coupons much better than those in MB, as you can set coupons only to operate on packages and not domains (e.g. providing 3 months free but charging for the domain).
As a billing system that is coded to be modular, (at the moment it only supports cP) it has cP integration that is almost as good as WHMAP's, and that's saying something.
Overall, we've found it to be excellently coded and very frequently updated, whereas MB had nowhere close to the upgrade cycle and the coding was in many cases less than perfect...