Guys, this edges the ridiculous and insane. This is not good marketing, guys, this is a very low and dirty marketing that not only harms your own image, it also scares the prospective (possibly paying) customer away for good.
If you want to charge, then for f*cks sakes, DO SO. But if not, then do the right thing and give the free plugin FREE OF NAG.
Sometimes it is better NOT to give anything at all than give this sort of crap to people!!!
As I said before, and as a matter of fact as I say for a LIVING, the free sample you offer customers is the business card of your business. No one is going to buy something and take home if the free sample tastes awful and looks terrible.
And nags like these just tastes awful and looks ugly too. Not to count that this is totally forcing your hand over people when any five year old knows you get more people with GOOD things. Nag is not good. Spam is not good. Subliminal blackmailing (acquire our other plugin or else we will make the administrative page of your WP blog look like hell with our advertisement) is definitely not good.
Its really a pity. The plugin is so promising. Pity I won't be trying, because you managed to scare me away. I am one of those who PAY when I like stuff, and I pay well, but I like my free samples to taste and look good before I so dare to invest my money.
And I don't invest in companies that subject other people to this type of "dirty marketing", whether they can or not afford it.