The main reason we had to stop using it was that the 'monitor IP' was just constantly marking our second WAN connection as down every couple of minutes and causing a constant failover before almost instantly failover again due to recovery.
It cause a lot of havoc with our users.
It was most likely caused by the Comcast Network (latency, network, etc), but it made it impossible to use the feature.
Some of the other products we reviewed had fields to set the Timeout, Check Interval, Health and Recovery Retries that allowed to fine tune the feature based upon various factors.
If something like this could be added or exposed that would most likely solve the issue with items such as latency, etc.