I just received a super cheap SDI to HDMI converter which I bought to mount on one of my HDMI monitors. I paid only $21 for it so it certainly goes in the super cheap bin.
It is advertised to take 5-12V power and I wanted to test will it work on a fresh off the charger V-lock battery (measured 16.8V). I can happily say that it works with no ill effects (like smoke).
I opened it up just to confirm and the input capacitor is rated at 25V and it has AMS1117CD voltage regulator. And it says 5V>>18V on the PCB, right next to the power input.
It also has a metal casing and it seems robust enough but there are few issues.
The BNC and hdmi connectors are not robust enough. If you were to use it in production environment I'd strongly advise to have backup. I am planning to change the BNC connector to a better panel mounted one.
Also, the pcb in my unit is mounted with one screw only although there are four screw slots.
I attached a few snapshots