I can attest that Speedify in redundant mode will handle a link failure in the middle of a Zoom call without a single lost packet or other impact. This isn't failover, though, this is redundancy; it's like having a 1 disk fail in a RAID1.
(I have a similar setup to the OP, but using an array of M.2 4G/5G modem cards connected to external antennas.)
Alex from Speedify here. Yes, we make a multi-path VPN tunnel, so that calls can be shifted from one link to another without glitches (apps see the same IP address the whole time). To make this work, we do some smart things like retransmit packets that were just sent on the failed link, on the still-working link since they were likely to have been lost.
So far, nearly every redundant link I've found seems to lead to bugs and glitches all round when failover actually happens.