Ideally, I need to be able to complete a test migration of the forum data to various candidate systems, free or paid, and see which one best handles my legacy data and which one best suits the specific needs of my forum.
The demo could be timebombed, it could put "this is a demo" on every page, it would still be really useful to go through a test migration of my forum and see what comes out the end.
I'm not going to pay $140 on the offchance it can successfully import my data and work in a way I and my users like. For example, Elkarte (an SMF fork) choked on old attachments originally added in SMF 1.0 which lacked a specific DB field added in SMF 1.1.
Just my thoughts as a prospective customer.