yes i have used it. it's completely worthless. most of these products are.
reality check:
1. although carbon on intake valves can and does happen, mazda went to great lengths to change how hot the valves get to minimize carbon buildup. it is VERY rare to be a problem.
2. if you're spraying this stuff into the intake, it's just not there long enough to do anything. if you want to go the chemical route, you need to soak the valves for a good length of time. there are products that are good for dissolving carbon if left to work for quite a few hours. most don't do much, you'll need to do some research.
3. the most effective method for cleaning out the valve carbon is to pick it out by hand and use walnut blast.
4. this is in no way part of regular maintenance. should only be done if there's a problem and reason to believe that valve carbon is the issue. at 40k kms i can pretty much guarantee that you don't have a problem.
