Don’t worry about the brake system if it’s for a 206. You won’t got through a set of pads in a 20 race season. I can shim my arrow brakes in less than one minute without hurrying. On the other hand the otk self adjusting system is the most high maintenance system I have ever used because they need bled frequently.
When looking for a kart used, price vs how old it is is important. Also, ideally you would like a kart designed for low hp, specifically 4cycle.