Otherwise, what you get is what you get with HostBill - if the canned product meets your needs, then great, but when you need to customize something.... it is what it is.
Not unless you have some patience and PHP skills

I've added modules to our installation for VATMOSS Excel file generation, IP-/account-based VAT calculation, completely revamped the domain order page into a multi-stage categorized selection with live domain checking, added custom PHP pages and a own template, added a translation engine to Smarty, added login-less access links for cPanel, added auto-away and desktop notifications to livechat, added custom registrar ...
Just saying you _can_ customize Hostbill. It does even come with a lot of nice hooks and a good plugin system, there is just n.o. d.a.m.n. d.o.c.u.m.e.n.t.a.t.i.o.n.
Oh... and quality control (or the lack thereof) is somewhat worrysome too...