The Inquisitor's spinning lightsaber breaks the rules of the Star Wars universe even with the massive suspension of disbelief afforded to the science fiction genre. These sabers should not exist in a galaxy far, far away. Let's look at the diagram of a standard ligthsaber:
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You will notice that the power plant of the lightsaber, the kyber crystal and power cell, are contained in the hilt. Now let's look at what happens when an Inquisitor's lightsaber spins:
(click for the full sized image)
How is this supposed to work, even in a universe with flying cars? The emitter is disconnected from its power source and the kyber crystal. I'm sure there is some credulity-busting in-universe explanation that somehow the power and plasma are being transmitted through the rotating ring, but the operative phrase there is "credulity-busing". Even in the Star Wars Universe, this is straining suspension of disbelief. So how is that some fans expect the HasLab The Black Series Reva Force FX Elite Lightsaber to be able to spin? The capability pushes plausibility in the Star Wars universe, so it would be utterly impossible in our universe even if it were a multimillion dollar defense project, let alone a $500 collectible. Force FX sabers have the battery in the hilt. How on Earth (literally) could a blade be lit when it's not in contact with its battery?
Like Yoda, sometimes Star Wars fans ask the impossible. And I didn't even address the fact that the saber is 6'5" long. If it did spin, it would a) be lethal and b) 95% of fans would break it when it slammed into the floor.
In case the intent of this article is missed, the purpose is not to throw shade at any at any Star Wars media. I think the Inquisitor sabers are fun, and I'm willing to suspend disbelief for the sake of being entertained. The purpose is to try to bring a dose of reality to the fans who are criticizing the HasLab saber for not spinning.