That process seems like it would slow down wireframing?
My thoughts exactly
You mean the stickers?
The whole process. I can draw rectangles and sketch icons a lot faster than searching a sticker page for stickers of rectangles. Also, wireframing is a living sketch, and changes often while perfecting. Moving stickers around a lot and searching for the perfect sticker just doesn't seem worth it. Just my opinion though. Good for them for getting backed.
"So for our first project we wanted to create a tool that is as fun to use as it is useful"
To me that really makes it sound like this arose from the fact that they wanted to create something, rather than they had an actual problem they wanted to solve.
That's probably also why it doesn't really speed up wireframing; Sketching works just fine already.
I like this one better Sketchy Notebook