We use modern bill, and its "alright" nothing can beat a in house programmed solution.
Modern Bill does what it says it will do, although it seems to do it in the most awkward way possible with us! We decided to use it because of its support for Plesk. The automation is a huge benefit for creating accounts, it allows customers to have account access within 20 minutes (or the frequency to which you set the API que to update).
Modern bill has its draw backs, it has no multi-currency support and a few other points that we would have liked and as you mentioned they seem to say it will be fixed in the next version
