I've seen both brands advertised on eBay with widely varying prices. I've long assumed that Italeri and Revell are, if not the same company, have a common owner, and that it's the same kit sold under two brand names. Am I right?

Same kit, different decals. Different model companies, but Revell reboxes a lot of 1/35 armor kits from various manufacturers (Italeri, Dragon, AFV Club, Esci, etc.). Unless the vehicle is a modern Bundeswehr armor kit, it is most likely someone else's kit in a Revell box.