Are you able to post details of exactly which serial adaptors you are getting? The feedback I get on the ASCOM groups is that a lot of people have problems. If there's a solid way of getting connectivity that would be really useful.
I have been using cheap Chinese made serial adapters without the slightest bit of trouble for about 6 months now. I didn't feel like paying $35+ for a proper converter when ebay had cheap china ones for $2.99 shipped.