Article says the system probably costs Mazda "several hundred dollars" a vehicle. That would have to be added to the sticker. That's a lot of gas where gas is $2/gal in the US. Meaning you'd have to drive for several years before getting that money back. Same type of consideration as a hybrid purchase, just smaller scale. In other countries, gas is 2-4 times the price making more sense for a system like this.
The other thing is, how good of an idea is this in a turbo engine where heat is a bigger issue? I personally wouldn't want my turbo engine cycling on and off, but I don't know enough about this to make that judgment. I just figure turbo engines run hotter and when the engine turns off, cooling is affected. Plus I read a lot of people online say they don't really like the feel of start/stop systems. They have a weird delay when you hit the gas. Perhaps Mazda's i-stop is better.