What do you think of 'em? I only have one so far (Warp's Edge), but it is cool. Being anal about alignment and symmetry, mats are awesome for me (even though I only have one). Having a "background" to the game space is very nice, too, since my table and/or tablecloth are boring and anti-thematic, as well. But, the mats are also 'space consuming' for storage, which has to be considered by me, anyway. There's also the cost, of course.
They seem to have too much of a "profit margin", too, but I think they're praying on us gaming addicts. But, probably a good marketing decision, though. Damn corporate bastards! They know us too well.
I really like them when they help with set up and when you've got to move the cards a lot on your table. The first one I had came with Legendary Encounters: Aliens and it's perfect.
I've bought two or three with Kickstarter campaigns, but as they are expensive as you say, and not always necessary or really helpful, I'm thinking about buying a large neutral one. A starfield perhaps.
I was lookin' for a large, neutral mat, too. My first stop was here, but I'm gonna keep lookin'/researchin'. Maybe I can find a better deal.