I've used these since they first came out, and they're fantastic.
The thing I enjoy most about them is being able to draw out different maps before the game and keep them ready to do. The flexibility is incredible.
When I ran War of the Burning Sky, the first scene is a tavern, which I drew out for the group. At a certain point it gets attacked, and the entire thing goes up in flames. I had a second copy of the map with those details ready to go. That doesn't sound like much, but the group really enjoyed the quick transition.
If you have your flip mat out, and the group decides to do something different, it's erase the whole thing and start over. Tiles? Just grab a new one. And of course if the group decides to go back to somewhere you've drawn already, you can just put the tile back, as opposed to having to re-draw everything again.
The second thing is how you can simply detach one of the tiles and either put in a pre-drawn map or just draw in the direction your group is going. Once again, flexibility is incredible. If you've ever had the GM start drawing a map on a particular side of a battlemap, you knew which way the encounter was going to flow. With the tiles, the action can flow in whatever direction you want, and seems more natural.
Finally, the older set has seen near constant use by me or other GMs in our group for about 10 years, and is still in good shape.
So yes, they're expensive, but I'd say they're definitely worth it.