I often make extensive feature comparison matrixes (example). I’ve been using WikiVS for years, and more recently, SocialCompare. Slant seems very promising.
However, services come and go. As much as I hope Slant will be around for years to come, my mind would be at ease before contributing massively if there was an option to export data.
Hi Dan! Welcome to the meta 
I’m one of the Slant founders.
We’ve been meaning to build this for awhile now, but with so many things to do we basically said “we will build it when someone asks for it”.
So thanks for asking for it, I’ll chat with the team in the morning and make plans to build this feature out. I’ve seen many user generated websites die and take the data with them, as much as I hope Slant stays around for years I agree it would be nice to have a data export. We’re on it.