1) is it hard to play fantasy on them? As in, does the surface of the matte make it hard to slide movement trays on them?
Of the three mats that Zuzzy makes, the 'despoiled reaches' is on of the best for using with fantasy (as far as playability). There is a good bit of detail and it is very low/ compact. You shouldn't have any problem sliding movement trays. With monsters or individual bases, you'll need to lift the figure, but that is going to be true with any highly textured game board. I would definitely steer clear of the 'verdant land', the rough grass is way too tall and any slightly off balance figure (standards, mixed plastic and metal, etc.) will constantly be falling over.
2) Would snow flocking crack or fall off this thing really easily when rolled up / any suggestions on how to do it?
If you plan to roll the mat up, steer clear of flock. As Blue Orphen said, the company suggests it's own method of painting the mats. With the sculpt of the 'despoiled reach' it should be very possible to paint as a snow board. Just paint the jagged rock as rock and the lava flows as snow. Adding flock to the board would just be covering up the benefit of a custom sculpted mat. Not to mention it would all fall off within the first few uses.
I think the Zuzzy mat is a great item, my only negative point would be the ridiculously bad casting quality. It appears as if they just pour the latex straight into their mold without any special treatment. This leads to air bubbles throughout the mat. As the mat is only about a 1/16th of an inch thick, it generally only affects the taller details, (especially on the 'verdant fields') and pretty much disappears among the busy sculpt, but there are a few instances on my mats where a hole passes all the way through. Honestly, unless you're using the mat in a tug-of-war, this shouldn't be a real issue, but I wish they would take the time and give the mats a little more attention when being produced.