I have nothing against GPL, but I do have an issue on their advocates using the term "Free Software, as in freedom." to describe their license.
GPL imposes a restriction on the use of the source. Since it imposes a restriction is not free as in freedom, because restrictive is the opposite of free.
Thus all the GPL being "Free Software", is just propaganda based on a lie. Is like, we are protecting your freedom, btw take this ball and chain, it will help us to better protect your freedom.
Anyway, I like this SimplePL license because it does not hide its meaning. Nor does it claim to be protecting your freedom while imposing restrictions on you.