To answer my own question, I found the following advice on the UK Keep Hearing site under Phonak CeruSTOP wax guards (claims to be the UK’s favourite hearing aid accessory store - so if that’s true, perhaps they have reason to know):
"Is it compatible with other brands?
The CeruSTOP wax filters are also found on other brands hearing aids. So do not worry if you are using these filters but are confused because your hearing instrument is from another manufacturer. As long as you need CeruSTOP, these will be fine."
So I ordered a 10-pk(80 units) of Phonak CeruSTOP’s on Amazon for $25.99 and will see how those work out. Don’t know much about the physics of sound but I’m curious that the holes in the wax guards don’t have to be aligned with the holes in the domes, etc.