Sometimes, I hate so much Freemium. It’s like giving a hope for someone but actually it’s gave another problem and headache. To force someone bought something that said free as from promotion is more like create hate because you force someone to buy something that were meant to be free, as your promotion.
As developer, if you want to create something for free than give as free and you will have reward after, if not from people which helped by you, than Allah will reward you for helping people. And if you want to create something for sell then sell it is. No hiding, no absurd and no gharar.
You create apps but you insert ads, what the ….
Just find another way for make living.
And more sad again, this method marketing is create by people who not understand a religion at all, which extreme people will said as khafir, this method is created by people who thirsty wealth and then Moslem followed them. Sad… sad…sad….
Just find living which exactly is for real, like your own creativity or your skill. You can sell WordPress themes, plugins or another thing that you create by yourself. It’s more will appropriate and get appreciate.
Otherwise, this is only my thought and if you have any other considered I will welcome to for you advice.