Yes, to get the same ppm N from a 5-5-5 that you would from a 10-10-10, you'd use 2x the amount.
In this case, being a 3%N formula, you'd need 13/3=4.333x the amount to provide the same nitrogen loading as the MSU.
HOWEVER, if the so-called "MSU" fertilizer you have is a liquid from RepotMe, it is improperly and illegally labeled as being 13-5-15-8Ca-3Mg. That is the formula of the powder they dissolve in water to make the liquid, not the formula of the liquid in the bottle, which it's supposed to be.
If I'm remembering correctly, they dissolve one pound of fertilizer in a gallon of water, so the formula on the label should be more on the lines of 1.4-0.3-1.6-0.86Ca-0.32Mg.
By the way, if you were to actually use the MSU powder at 2 tablespoons per gallon, you'd be applying over 1000 ppm N and would kill your plants. Two tablespoons of that rip-off liquid would be about 110 ppm N.
Thanks Ray!! I called repotme, and they confirmed this.