I've done some testing and it seems to be a little picky about its power source. The converter works fine with a 'proper' HP Procurve managed switch, but with a Netgear Prosafe switch the power light pulses on and off and the USB cable doesn't power up.
The converter is also lacking the molded tab to prevent the RJ45 from snagging shown in the picture above, so I'm not too optimistic about how long it will last before it needs re-crimping. I'm considering opening it up and placing it in a new enclosure with a proper USB A female socket to aid compatibility with other devices such as iPhones.
Overall for £5.19 I can't complain too much. I will use it a little more 'in the field' and do some load testing and follow up in another post.