To build on @MartinLangmaid’s answer: As it happened we were recently running an HA pair of B380 + B20X (after a backup B380 died on us). It works splendidly as long as you are accepting the fact that you have to keep the two in sync manually (rather than automatically, as would be the case with two identical devices).
We found that we could get close to automatic synchronization of (the key) elements of the configuration by means of IC2 and an appropriate tagging of features.
Test “failures” of the B380 switched control to the backup B20X with nary a hitch.
Having said all that: We are reverting to having two identical devices as our HA pair, principally because of laziness (avoiding even a small bit of time and mind-space for proper sync maintenance is worth the investment in our use case).
Good luck,
Z