I have been trained the use of these bags, and they are a very good idea if you happen to be working on a fire. Even then they are a last resort measure, and are far from infallible. Deploying them is a definite indication that someone screwed up.

If you are not working a fire, you should be setting speed records as you depart the area quickly. Bear in mind that a wildfire, when conditions are right, can spread much faster than a human can run, much less walk.