Thx for your reply and the linked thread.
I suppose I wasn't really expecting anything official or definitive, just people's experience - most of my kit is based on other people's recommendations at some level.
FWIW On a desktop PC I am using an "Alfa Network AWUS 036 NHA", 150 Mbps, 802.11 b/g/n, where it is using kernel module "ath9k_htc". Just plugged that in to the Libreelec box in place of the Edimax, configured it and rebooted (presumably using the same kernel module here), and it seemed (without detailed tests) to bring up the network and to run fine, giving me better range than the Edimax (ancient) dongle. Not "ac" but likely adequate for what I need, so may just get another one.