I would worry about this too. It seems like you could get bogged down using a tool like this, spending days creating pixel perfect mockups, just to throw out your work later. That might be why Balsamiq is such a popular tool; the mockups look like ass, but they let you iterate quickly without caring about the tiny details.

At some stages you may feel the need to create pixel-perfect mockups. Especially when you are working with remote teams you don't have other way to specify how your product look like to developers that don't pay that much attention to details.

Besides from pixel perfect I've been missing a product that allow me to be "screen-transition perfect" since being sketching on omnigraffle / sketch and having to use another product to mockup transitions is a really painful process.

It seems that the primary purpose of this tool is to add interactivity to designs. I don't think it replaces the need for mocking before you design for purposes of rapid evolution — I think paper still wins in this area.