It's a good system, but I would never use it myself.
A very long time ago, Blizzard and I discussed the practicability of larger tilesets as opposed to the time they consume to create the everyday maps for your game. I prefer standard size tilesets. Everything included in the originals is all that you need. It really is. If you want to make your game more original, then sure ... add a couple tiles, but you don't really need the mergers.