4-in-1 Remote RJ11 RJ45 USB BNC LAN Network Phone Cable Tester Meter

Q: Does this work for cat 6, 6A, and 7?

Yes it will. This tester checks for continuity and proper wiring. That is, it checks that "wire 1" goes to "wire 1", etc. The differences between CAT-6 and CAT-7 cable are due to construction, shielding and maximum bandwidth (that is, how many megabits per second it can support). This tester does NOT check, for example, if a CAT-7 cable can handle it's full design data rate. All it does it to check if the cable is wired correctly. Hope this helps.

Q: What does the "crossover" display mean?

means that the cables are crossed for a point-to-point connection without swicht or o router

Q: Does this work with USB 3.0 cables?

I've never used the USB tester portion before. I don't see why it wouldn't, your just testing for connectivity. I do know you can use USB 3.0 devices in USB 2.0 ports. The difference will be connecting a 3.0 into a 2.0 you will NOT get the speed benefit from a 3.0 port. USB 3 is 10x faster than a USB 2. I know this didn't answer your question directly but I hope it shed some light.