Josh from NCH replied to me that Basic is for Home, uncommercial use, whereas Pro is "unrestricted"; he wasn't any more forthcoming than that about what "unrestricted" means in terms of how many PCs you can install one license on. My understanding is that you can basically install it on your PC and a backup unit, like your laptop, but you can't use them both at the same time.
I've been using ExpressScribe for something in the range of 20 years, satisfactorily. It's more or less the gold standard for what it does. That said, NCH's care for its clients is indifferent to lousy. I can't complain of having been ripped off, as some other complaints may be, but the lack of cooperation or concern is outstanding. Its latest email promoting V6.06 Scribe is typical, saying it has lots of improvements and features, and to "learn more" at such and such a link. The link is only the Scribe webpage, and says nothing different about the new version.
Still, Scribe, at least, allows you quite some time to test out their full Pro version before deciding whether to go with the unlicensed version--audio only and that restricted--or Pro, which includes a wide range of audio formats (if you're going to be using those) and video, which can be very useful if the speaker is using a slideshow.