When I tried to use the E-Machines ethernet daughter card for the Futura II SX the machine locks up during extensions loading if I try to use Open Transport. I had to switch to Classic Networking to get the machine to boot. I've only tested it in the IIci and it was with the 10baseT version of the daughter card.

Other items of interest...

Asante made a version of the MicroAsantePrint (ancestor to the AsanteFast, LocalTalk/Ethernet bridge) which came with a thinnet port as well as 10baseT (only one port active at a time).

There were also Asante thinnet AAUI transceivers. So for those Macs with AAUI, one could put them on thinnet media if one had those transceivers. I once bought a batch of transceivers expecting 10baseT and received thinnet. Asante was a peach and replaced them for me.