The program does not exactly cost $5/month.
If you download the program in the first month of your subscription (which costs $5 + tax) you can keep it and it will still work indefinitely i.e. it has no DRM
This is WAY different from other subscription-based programs, that have to validate your subscription status via internet to keep working
Here if you are fine with the functionality the program currently offers you can cancel the sub after the first month, So you only pay the subscription to support the program development and receive updates and standalone Windows patches that are the result of the development you supported.
The developer(s) have already made and maintain another freely available solutions like Supermium and I think it's fair that this one requires the sub of this kind.
If DRM was to be implemented I would very much have to reconsider supporting the project myself, it would be ironic for people who claim to fight forced obsolescence to make programs that become bricked whenever they feel like no longer supporting them.