There is no problem ever after having a hot motor for the guage to read over the half way mark. If you are getting the red-line during normal conditions, it wouldn't be the coolant in the radiator.
I personally don't waste money on expensive coolant fluid. What I use? Premix $3.99 coolant from Autobarn. Works just fine for me.
I bet a million bucks the turkeys at the dealerships don't use expensive **** either, but charge $45 for a radiator flush!