What will I really see a s the major differences in using the Aircable vs a CF bluetooth card?
The reported power consumption of the Aircable is significantly lower than those of CF cards.
The Aircable is more vulnerable to being damaged/damaging the Z if dropped.
Are teh speeds the same or about equal?
No: the Aircable runs at 115.2kb. Some CF cards run at only 57.6kb, but some can also be set to higher baud rates. This may or may not matter for your purposes.
Now we get to the fun part: the Aircable
might be able to do a lot more than simple replacement of a single serial cable. E.g., sending/receiving audio, or maintaining more than one connection at once (you could program your Z to automatically dial your cellphone, and make obscene calls in a synthesized voice ).
Or it might not: Aircable is very vague about the capabilities of the Z model (or even about whether there's more than one model). If all you want is a simple serial link, that doesn't matter. If you want to do more, you need to investigate further.
Ran