The pan shown is one piece. I have not used that particular one, i purchased the 3" and 2" pans seperately.
I purchased the individual ones b/c I wanted the option of using only one if I wanted to. But you could always cut them apart just as easily.
I find that the 2" is hard to ice on it's own, so maybe in the one piece shown it would be easier to handle and ice (but this is just an assumption)
As for the pans themselves in this size I really like them. They are handy for that little extra batter (makes a nice snack) or something to help build up a section on a cake if needed to make hills or other fun stuff.
I liked mine. I had only used it once ot test it out. I had some leftover cake batter. I didn't grease the pan very well. Some of the top layer stuck in there. Live and learn!
I bought one of these and just used it for the first time tonight. I actually filled it just slightly more than 3/4 full and ended up with another 1/4" of cake above the top when it was done baking. It's a very generous single serving of snacking cake, especially if you use the Chocolate Stout recipe and eat it warm just out of the oven.