Better than no brakes? Not by much. Bugger all for clamping pressure. You have lots of options, even free if you're resourceful. You can use a hydraulic setup from a bike, car, sled or quad if you can source it free or cheap and have a little mechanical inclination. There are mechanical calipers that can be had for fairly cheap, too.
Three quick examples for you-
My kart- Hydraulic Clutch Master Cylinder (yes, clutch!) from 80's Toyota pickup truck, and caliper from 80's Mercedes (both scrapyard finds)
My Kids' Kart- Hydraulic Brake Master Cylinder and Caliper (front) from 1988 Yamaha XV250 Virago motorcycle.
Here's another lo-buck idea- awhile back, a few of us were batting around ideas for a home-built mechanical brake caliper using either a large C-clamp or woodworker's clamp for actuation, search around here, you should be able to find some info.
My kart build in progress- Hydraulic Brake Master Cylinder and front left caliper from 1984 Honda VT750 Shadow motorcycle