"surge disc brakes are superior to electric drums"
Depends...
Pros:
1. Surge brakes don't require a brake controller and all the installation involved, so they are easier to install and use on multiple vehicles. Can use the cheapo 4-pin connector. Great for rental equipment.
2. In some cases, surge brakes can generate higher braking forces.
3. Surge brakes require no adjustment - they are automatically proportionate to vehicle deceleration.
4. Surge brakes have no battery (with accompanying charging and maintanence) required for break-away safety. A simple cable is attached to the tow vehicle to activate the cylinder by pulling the cable if the trailer comes off the hitch.
Cons:
5. Surge-brake actuation is by tow vehicle deceleration, not brake pedal position. If the tow vehicle has no traction (hydroplaning in a big puddle, or on snow/ice), and can't decelerate all that well, then the trailer will just keep pushing it. Not so safe in rain or on snowy or icy roads. Been there, done that! Note that some electrical brake controllers also use deceleration and not brake pedal position and will have the same problem!
6. Surge brakes break-away safety system is typical cuplrit of stuck-on failure. When dropping the trailer, its easy enough to forget to disconnect the break-away safety and attempt to drive away. After you notice the trailer is still attached and stop and disconnect the safety cable, the next user of the trailer will have stuck-on brakes because the break-away safety is a ratcheting mechanism that needs to be RESET! If they are only partially stiuck-on, you will just burn up your shoes and have no brakes when you need them. If they are really stuck-on, you can burn the whole trailer to the ground as was mentioned.
7. Actuation cylinder can stick on, but I bet this is usually caused by #6, above.
8. On some systems, a manual lock-out pin is used to back the trailer up a hill. Its easy to forget to remove the lock-out, and you can have no brakes next time you use the trailer. Better systems have an electrically-actuated lock-out valve or pin controlled by the reverse lighting circuit, but this requires more wires than the cheapo- 4-pin connector.
9. Surge brakes have no braking in reverse. This can be a problem when backing down a steep hill. Kind of interesting backing a large boat down a launch ramp into a lake - it feels like the boat is sucking you into the water when you put on the brakes. Luckily, it stops once the boat starts to float!