Controllers (Official name: 共游机, literally "Multiplayer console", usually mistranslated as "Swim controller") have a darker color than the iQue console-controller and they can be bought separately or in bundle with a multiplayer adapter (Family Pack) where you can add up to 3 other players.
They are nothing more (or less) than a N64 original controller.
The iQue output +5V on the controller's connector but it is unused by the controller. So games might still be compatible with rumble pak if nintendo did not remove support in their software. With this +5V output they could have released an iQue controller with build-in rumble support. Information retrieved here.
Both Captures were done on the iQue Player using the iQue MSK Project.
Top: Horipad mini
Bottom: OEM N64 Controller
Due to the iQue Player not having a PIF like a standard N64 its functions have been moved to the SI.
This change causes that the iQue Player Polls the Controllers at the same time unlike a regular N64.