Failover on these is very hard on internal devices with already established streams.  Basically it is a terrible experience unless you reboot the devices, force a wifi reassociation, or reboot the router.    

I have this setup with 2 ISPs using load balancing and failover.     

I had this setup before with a Cisco ISR and had a similar experience there initially.  the way i resolved it was running a single layer 2 transit network for both next hop ISP connected routers and  not running nat on the failover router.   I had OSPF running but i could do it with just static routes on the next hops w/o issue.  I would still be running that setup but I have upgraded the circuits and i would need big iron on the Cisco side to get the through put of the new connections.   

This little box is plenty fast but seems to be limited on how you can set it up for this purpose.  

There does not seem to be a way to do this or something similar that I am finding.    

Also there is dosent seem to be a way to configure the tracking frequency of the wan connections - they seem quite long right now 30-45 seconds before it notices its down.