The big downside to surge brakes, is in slippery weather the wheels can lockup during braking, but to unlock the brake you have to give it some throttle to take the pressure off the master cylinder! And on steep downgrades, they can drag the whole way down until they start smoking (we had this problem with our boat) especially if you are engine braking.
Upside of course is no controller needed, which is especially useful if you want to tow it with multiple vehicles. And disc brakes are superior to drums for heat rejection, and surge discs are only a small upgrade over surge drums. But electric-over-hydraulic discs are a $$$ upgrade over electric drums.
