Just curious: How is a unit defined? For each copy of it? How should that be measured? Or for each download? That can be very inaccurate if you have your product on a lot of independent mirror servers.
If you are distributing a proprietary bit of software you presumably have a method for counting how many copies you sold in order to know how many $ you should have. If you are giving it away then why not just use the GPL version
Yes, I would probably choose GPL. But there might be some people who will not. Maybe even only as Freeware. Or maybe the software itself for free but you pay for some kind of service. In that case you could even use multiple instances of the software at the same time from a single account. Is that all counted as one unit? Because again it is probably impossible to count the copies of the software. That is why I was wondering what "unit" exactly means here.