We bought ours new, mostly because I needed it right away and could get free express shipping with Amazon.
I've got no idea how the different models compare with each other - I basically bought mine on my brother's recommendation to fit an odd-shaped doorway in our house, with no consideration to using it in conjunction with more pieces. (Of course, I didn't think my DH would object so strongly to hard-installing it, and it's kind of useless to just set up, so I feel like I wasted $80. But that's another story.)
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Liz
DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle