It is my guess that you want a lot of people to type the sentence once. This would result in a sample of typing skills. I would expect people to improve or at least change their typing actions slightly if asked to type the same sentence more than once.

BTW: That sentence is known to contain all 26 letters of the English alphabet. It should be typed with the second the replaced by a, making it slightly shorter.

Another (and shorter) sentence containing all 26 letters is.
Pack my box with five dozen liquor jugs.
I have never seen a shorter sentence with all 26 letters except for poorly constructed sentences, or ones containing proper names, or ones containing incorrect English words, or ones that did not make good sense.