I used that crap once and plugged off a new heater core I had replaced not long before. I filled the heater core with Muriatic acid for about 15 minutes. It flowed much better. I don't know if the whole system would be safe with it.
One other thing I've been told about is to put Calgon water softener in the cooling system and working it for awhile. I tried it and a lot of brown crap came out but I don't know if it would take out the Bars Leak.