Ok, lots of research here.
Vet recently gave me Comfortis for flea and tick prevention, when I raised concerns about the topical meds and the dogs gnawing on each others necks (where topical meds are applied.)
I also recently got a message from a friend who's dog has started getting seizures and is looking at other options...
So now I begin the research myself. Not making a decision yet, but looking at options.