I couldnt help but notice the similarities in the file names that are used by this free plugin and the one of a very similar name that wpmudev sell for $39 per month. I really think that $39 per month is a hell of a steep price for such a plugin, especially when you can get it for free.
While this seems to be legal according to the license, it is not really a very good practice. I just thought you may want to know about this, if you were not already aware.
In the wpmudev version, it even states within the coding "This program is free software" even though you will have just paid $39 per month for it.
It then goes on to state "Based on an original by Donncha". I suppose that depends how you define "based on" as it seems to be the exact same plugin with some updates and changes added. I would have thought a more accurate term would have been "forked from" as "based on" makes it sound like they only took the idea from you instead of the entire plugin prior to adding modifications.
WPMUDEV has had 12,806 downloads of this plugin. As the smallest single payment that can possibly be made for this plugin on their site is $39 and assuming that everyone cancelled their account after the first payment, which I am sure they did not, that means that WPMUDEV has made a bare minimum of $499'434. Almost half a million dollars!
Have you received any payments from WPMUDEV as a thank you for the initial work that you put into the plugin that they then took and made all this money off?
Hardly seems ethical unless you are part of the team who helped them program it.