Using this on-camera color viewfinder is easy. Just connect it to your camera with the included connection cable. You're all set to use it for your shooting. As for the power button, even though the keycap is missing, don't worry about it affecting how it works. When it comes to maintenance, keep it clean and dry. Avoid exposing it to extreme temperatures or humidity. If you notice any other issues, feel free to reach out for further support.