We tow a Honda CR-V four-wheels-down. I believe the brake capacity of our conversion is more than adequate for the toad 99% of the time. I researched weight-limit laws and concluded that I could probably get away without having a brake system on the toad.
BUT, that 1% chance was the catalyst that caused me to get an SMI Brake system. It includes a breakaway switch and an indicator that tells me when the toad brakes are applied. The toad brakes don't come on very often but there's some peace of mind knowing my braking distances are shortened a few feet in a panic stop.
For more info, see:
Weight Limit Laws and
Tow Bars Unlimited.
Another helpful site is:
SMI Manufacturing.