Mate theyre both coffee machines, and they both work fine (or atleast they do when you buy them new).
You simply need to make up your mind whether, now that the opportunity has presented itself, you want more of the same (as in another BZ99), or whether you want to try something different. Do you ever buy the same car twice, or the same TV set, toaster, lawn mower, whatever* :)
Thats about all there is to it.
That said, I personally wouldnt buy either of them as I would be looking to "upgrade" a bit when moving from one machine to another.......its the natural order of events.
At the used price level you are looking at however, there could be any number of differences between them from the point of view of age, condition & previous use.
See if you can ascertain that whatever you are looking at, is fully functional. As long as that is so, the rest is easily taken care of.
Hope that helps.
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