We are using blesta from 2014 and before that WHMCS was billing platfor,tryed CE and Blesta and chose Blesta. Now expecting 4 to go out of Beta ,yes it doesn't offer some integrations that WHMCS has ....it is price.
But it is really stable and dev. frendly...i tryed everything out there and when I started with local business I wanted Hostbill or WHMCS,I starded with WHMCS and after few years migrate to Blesta.
Today we have only few options really worth to look...in first WHsouite looks promising while they in beta but they turn to OpenSource/free ....which isn't bad by itself but can't expect anything more than basic features