No, you can't. You can download the source code and build it yourself, or you can download a binary demo, or you can pay for a binary.

I used this tool a lot on Arch which had PKGBUILD for it on AUR but I wasn't able to build it on MacOS.

But you don't have to pay for a subscription. You pay for a binary plus x months of updates up front--it's not subscription software.

To be fair, it is described as "Expires in 6 months" on the purchase page which makes it very unclear if the binary you downloaded is going to stop working. If it does stop working then it's not unlike subscription software.

I was actually vaguely contemplating purchasing it until that uncertainty made me think paying them might give me something worse than free (ie: something that would break at an inopportune moment in 6 months).

I can confirm that the binaries do not stop working after the 6 month.