To someone cleaning up rusty parts, I'd say it is. I have some beautiful-looking brakes on my Peugeot now after an overnight soaking. It really takes the elbow grease out of the job. I'm not saying that Evaporust is the only product or the best or whatever, but for the OP's purpose of cleaning up those old caliper brakes, it would do great.

You are right, though -- it's not cheap. In the US, it's about 20 bucks for a gallon jug if I recall correctly. It can be used more or less indefinitely, though. I haven't found its effectiveness to wear off with time or use. I have a couple of small containers that I've used to soak various smaller bits and I've done that 10s of times with good success each time. I still have half of my original gallon in the jug for future use.