The payment for Bet Angel is on on-going payment. We would only consider doing a one-off payment if we were running down the business or didn't intend to invest in future upgrades.
We are committed to constantly investing in new services, the community surrounding Bet Angel and, in particular, introducing new features and upgrades to the software. You can see this from our release history: -
Unfortunately, we can't achieve that with a one-lifetime license fee. We need to match revenue to future upgrades and opportunities such as the new features Betfair are planning in the next 18 months or so.
If we had no plans to invest, then a lifetime license would work. But as it is, we plan to invest heavily for the foreseeable future so our existing pricing will remain as it is.