cz75b: The advantages are higher round capacity and a pinkie grip on the bottom of the mag. I like the pinkie grip on the mag for my hand. But if that is not important to a person, the CZ-75 mags are less expensive even though they don't hold as many rounds. I carry for defense, so the one more round is decisive for me.
Personally, I will never do business with CheaperThanDirt because they gouged during the ammo shortage.
But the Grabagun deal you linked is a good deal and I have bought from them before.