Finally one that works!Both the transmitter and receiver units are well built and feel sturdy. I've tested using a CAT7 cable over 20 metres, and it functions perfectly. The picture quality is accurately replicated, and audio is entirely in sync. I'm using this to operate interactive media presentations from a computer upstairs, to a TV in the lounge (connected to a sound bar). With the KVM functionality via the included USB Type A to A cable, I can control my computer in real time, with no noticeable input delay. I considered using an active USB extender for this purpose, but the ability for the data signal to pass through the units via the CAT cable is very convenient, saving needing another cable running in parallel. Previously I wasn't aware such technology existed until discovering about this type of unit.I previously had a less than ideal experience with another (cheaper) HDMI extender product, where the audio was glitching no matter what, and picture was flickering with noticeable visual degradation. I've had no such issues with the OERI 230PRO here. Powering both units is required, and upon doing so there are two blue LEDs on each. As the included manual states, the lights are solid and don't flicker when the connection is established (one does when keyboard or mouse inputs are sent and received). I didn't need to press the Reset button as the unit synced everything up by itself automatically, but that is an option on both units if needed.The only thing I had to do on my computer was enable sound to the connected TV downstairs. On Windows, this can be done inside the Control Panel under Sound settings. Setting that as the default device is what I did, and then it fed audio signal via the HDMI cable output to the transmitter unit. I powered down both units prior to disconnecting the HDMI input and output from my computer and TV respectively.For the CAT6 or CAT7 cable itself, I went with a reputed brand for assurance about this. A key part is making sure the cable is of the EIA-568B specification, and also is a "straight" type. I did some research on this, and basically it should apply to any labelled as a "patch" cable. It relates to how the wires are, and then need to match up and not cross over. The manual states how otherwise the unit enters a protection mode and won't function until a correct CAT cable is used.Also go for full copper and not CCA (Copper Clad Aluminium). This is very important I read for power-over-ethernet functionality, along with longevity of the cable itself. Although CCA might be cheaper and work initially, there are known issues with those and not worthwhile.I've only used a CAT7 myself, but CAT6 will work fine. I'm unsure about CAT5e whether it'll have a sufficient frequency bandwidth for a 4K signal, especially over longer cable distances. CAT5e might be alright in 1080p and at lower supported resolutions, but I've not tested this personally. As I have a 2nd screen on my computer, I didn't need the loopback functionality, but this is a handy feature which is nice to have (along with the 3.5mm audio jack port from the receiver unit).Also a note to those like me outside the USA who might be interested in this item. I contacted OREI support (via their website) prior to purchasing, to ask about voltage compatibility. In very swift time they confirmed to me both included 5V adapters are dual voltage, and work around the world. I can confirm with being over here in the UK (which uses 240V mains supply) how this is the case, and it says this printed on the adaptors themselves (120V-240V). All it needed was a standard plug adapter (no need to convert voltage).Of course, if you're purchasing for use in the USA then it'll be fine to plug both units straight into the mains as normal. The adaptors are able to receive 240V and convert the voltage to the required 5V for both units. They were only ever so slightly warm to the touch after use for over an hour, which is well within their stated operating temperature. Beforehand I was a bit concerned about how they would fare with both being powered, but it's absolutely fine and perfectly normal for data processing units of this type.Overall I highly recommend this OREI HDMI 230PRO Extender. It's neatly packaged also in a sturdy yet easily openable cardboard box, and all components are contained within. If in doubt about which to purchase, it's well worth spending that bit extra to receive a proper quality piece of kit.