Hidden MMR is stated to be a very complex number which is likely a fractional number. Even I don’t know what an MMR number looks like but I would anticipate its something like “0.49906968587278295”. Skill Rating is your “readable” number and it follows your MMR relatively closely.
In the end, your skill rating is going to be very stable and accurate to your actual skill as long as you are playing consistently to your actual skill.