I picked up an old style Testo 523 last year at the RSES international conference. Got em cheap in a silent auction benefiting Special Olympics.
Other than there not being anything to do with the hoses, it is a very solid unit, better than the new style in some ways.
I mostly just use them as a backup to my Digi-Cool BTD-1000 and new style Testo 523.
The big question I have is, if I buy the software and computer cable for it, will it work in 64 bit Windows Vista? My convertable tablet and desktop both run 64 bit Vista.
While I don't have any particular plans to datalog anything, I'd like to have it as an option.