If you happen to be the 1 in 5 that it really works for, it's still not a good idea. I don't like it. It doesn't just stay in the radiator, it goes through all of the cooling passages in the engine too......and I just don't like the idea of that.
I've never heard of the radiator shop that I use charging more than 40 bucks to fix a leak in the tons of Jeep radiators I've sent their way.