This looks great. I noticed the "try it for free." Are there plans to turn this into a paid product at some point? How limited is the trial?
If you could come up with some scheme that was usage-based rather than time-based, you might make more money in the long run. $5/screen? $50/project? I dunno.
Maybe $100/year, upfront, non-recurring. That wouldn't be terrible. It wouldn't feel like time-based usage because the timeframe is so long.
You might be able to learn something from the pricing experiences of the mockup tools like Balsamiq and Mockingbird.
An instructive question which was asked to me recently: "Who would be excluded from using this project if it cost [I'll fill in price points: $39 / $99 / $199 etc], is it in their best interests to use this, and do you seek their business?"
Subscriptions work, everyone understands them, there is infrastructure to support them. Just sell them. Do not get cute with your pricing model without a very good reason, backed by data.