I'll take this one - ofcourse you still have to test your batteries. Since these regulators are very closely matched to each other, it provides for a very even load balance between the redundant battery packs when both batteries are healthy. Once you have observed that behavior, it makes it a simple matter to monitor each battery before each flight to assure they are tracking to known behavior. It also lets you more easily determine battery health by making note of how much you put back into each pack when re-charging. When that behavior starts to change, you know it's time to look at whether a battery is going south on you.

I should also add that you will survive a complete failure of any one battery, wire, etc. That's the key to this configuration. And the regulators are all failsafe in design, so switches aren't ever going to cause an issue.

Another feature is that they are very low dropout voltage regulators, so it is more likely that even a single battery / single regulator configuration can survive a one cell failure and let you land safely, since only a couple of tenths of a volt is dropped across the regulator when the battery voltage input to the regulator falls below the pre-set output voltage. For example, a LiPo pack has a cell die, but is still capable of delivering current. You have about 4V left to work with. The output of the regulator will be 3.8V, enough to get you home in a lot of cases.