most kits, dont have a torque arm when you purchase the kit, you get a torque washer which fits the wheels axle and that in turn slips into the dropouts on the bike. I have built and owned a few e bikes before i went gas, always had a torque arm never got electri- fried !!!!! Adding a torque arm does not increase your chances of getting fried , loose wiring in the motor that comes into contact with the steel frame might make it happen....
Torgue arms are a valuable addition to any electric kit, last thing you want to see is your wheel spinning off or ripping from your dropouts, the wheel in turn will rip your wires apart (FACEPLANT ANYBODY !!!!) and ruin your kit.
I have had kits on alumi bikes too, so long as your careful and dont blast the throttle from a standstill ,they work just as fine as steel forks.
The reason for more 26 inch kits.... easy answer... more 26 inch bikes and universal parts, 700c ( road bikes racers mostly) more specialized size and you have to hit the bike store for specfic parts.
I am about to build another bike for a friend in a week or so, 36 volt kit with a nice ping lipo4 20ah battery, just waiting for the parts to come in and then find a good donor on craigs list....should be a sweet ride at a sweet price, man i could build my dream cruiser for the cost !!!!
DUI cost him his license for another 2 years so realibilty is what i am aiming for.