Ya, that's weird about the spintec. A lot of guys at our track use them with no troubles as long as you make sure you balance the cells with a balance tray. When you use a high amperage discharger such as the spintec, you train your batteries to give max punch for a five minute race. If you just discharge it with the smartray(3 amp discharge) you train the cells to give steady power for a long period of time. Maybe your friend thought that the spintec cuts the runtime of the cells, which is its purpose. The 4200's can give nice power for more than 5 mins and you use the spintec you concentrate the power to give full power in 5-6mins and then drop.
Promarch 4200's, Orion carbon 3200
Novak GTB 13.5