This is indeed a very good way of setting WAN interface priorities in Speedfusion tunnels which I used a lot on much appreciated suggestion of Martin.
For SFC with its 6s failure detection there is one big drawback: when your preferred link is saturated, the traffic will be re-routed over the “backup WANs”: the ones with the unreachable low latency limit. This causes a drop in the traffic of the preferred but saturated WAN, which might in turn cause again a drop in its latency or packet loss, causing again (after 6s) a switch back to this preferred interface and thus a 6s endless switching loop…