It depends a little on how deep the integration goes, but certainly, building a billing system from scratch is a load of work (I've done it a couple of times my

It depends a little on how deep the integration goes, but certainly, building a billing system from scratch is a load of work (I've done it a couple of times myself), and you'll do a rubbish job of it. The sort of billing engine that you need to fully handle saas requirements, and especially enterprise as you say, is definitely not the sort of thing you knock up in a couple of weeks. Just ask the guys and Chargebee to find out how much work it really is. You probably couldn't even build the coupon component of it in a couple of weeks. Having said that, integrating something like Chargebee's offering into your own product shouldn't take that long and I'd argue that if you're building a company, there are plenty of more important things to focus on before you need to even look at billing systems — Xero will get you a long way.