This Movek myMix personal monitor mixer is a great option, but note that it doesn't come with a power supply. However, it can be powered through PoE. There's a minor issue where the main knob cover is missing, yet the knob still works just fine.

Using this Movek myMix personal monitor mixer is straightforward. First, since it doesn't have a power supply, connect it to a PoE - enabled source to power it up. When using the main knob, even though the cover is missing, you can still adjust the settings as normal. As for maintenance, keep it in a dry and clean place. Avoid exposing it to extreme temperatures or humidity. If you notice any further issues, check the connections and ensure the PoE source is working properly.