If you use u joints, they have to be in pairs, and the driving and driven shafts have to be parallel (straight in line works too, of course).
If you have 3 six inch extensions and 2 universals in your toolbox, you can experiment.
If everything is in-line, there's no issue w or w/o universals.
If I/O are parallel with the universals at significant angle (like 45 degrees), note that the "driveshaft" rotates faster 90 degrees, slower 90 degrees, faster, slower, but the second universal cancels this such that I and O rotate same.
If I and O are not parallel, the second u-joint does not completely cancel the first, and there is vibration as the whole car is asked to go faster / slower / faster ... as the driveshaft rotates.
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