[NTLK] USB Serial Adapter: Which?

Hi there from a new Newton owner, apologies if this question has been
asked millions of times already :-)
I am needing to buy a USB Serial adapter for use with my 2100 and
iMac and am wondering if it matters what brand to use. I have seen
on this list many references to the Keyspan one, but will a cheaper
one work instead? Ebay have heaps for only a couple of bucks
compared to A$65 for the keyspan.
I already have both Mac and PC type cables and the dongle is on it's
way.
Thanks in anticipation
Kate

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