What the heck are we talking about again?
Mu reports? Personally, I don't like them much. I don't know how many times we'll be landing in Cleveland and the ATIS reports show consistent Mu values such as 42, 40, 41, yet arriving aircraft are saying, "Braking action fair to poor." However, there are times where they are consistent with what is being reported by arriving aircraft. So, I'd say Mu values are just one tool to be used in determining if a safe landing can be made.
I will always value pilot reports from prior arriving aircraft above all else. Of course, you need to take into account what type of aircraft was in front of you, because just like in turbulence, braking action can be variable for different types.
I absolutely take into account runway length, width, grooved or ungrooved surfaces, time since last plow run, and precipitation intensity. If the plows are having a difficult time keeping up with cleaning off wet, slush-type snow, then that might be a signal that the runway is likely to be slippery by the time we put our tires on it. If it is a dry, blowing snow, that signals to me that we might have a less likely chance of poor braking action. Also temperature plays a part, because temperatures around -3C to +1C can make for a more wet snow, especially at places like GRR, SBN, MDW, ORD, CLE, BUF, etc. that are near large bodies of water. Very low temperatures like -15C mean that the snow is usually cold and very frozen, and less likely to be slippery. No absolutes here, of course.
So, while Mu reports can be valuable, there are a multitude of other factors that come into play in making a decision if a safe landing can be made. I am no expert on this stuff, but this is just my personal opinions based on my experiences over the past few years flying quite a bit in the frozen muck. Especially in YYT, YHZ and YQM.
Also remember, even if you can make a safe landing, you always need to make it safely to the gate. I've had many situations this past winter in the left seat where the landing was great, then it became treacherous on the way to the terminal. A few months ago in CLE we actually had zero braking action at a taxiway intersection. We were going maybe five knots, and when I started turning the tiller the airplane kept going straight. Applying the brakes to keep from going into the grass, at first nothing happen, then they caught pavement. Not a good feeling!
I will say, just to keep this "on topic," I am happy to know that if we did slide off a taxiway that horrible day, we have ASAP protection here that would help us learn from it, rather than it be a debilitating blow to our careers. I'm sure the Pinnacle crew in TVC is happy about that as well. Again, it is career insurance, all the collective bargaining rhetoric be damned.