It’s kinda disappointing to hit a subscription screen right after sign up, wasn’t expecting that. I definitely would not try out a social network with a subscription fee without lots of experimenting first.
I kinda expected that -- they promise no ads, and they're going to host lots of big photos. How could they possibly offer that for free? I agree though, the subscription model should be clear before signup, without offering a few months for free, they're going to miss a lot of conversions.
At the beginning it can be better to focus on the people willing to pay up front. It allows you to test the market and to focus on the feedback of paying customers.
You can add free trials and optimize for revenue later.