Good point on the airflow side of things, will have to see what other venting on the case there is.
Seasonic SSP-300SUG is sort of similar in so much that it has a connector at the rear rather than loom exiting a hole.
This does have PCB exposed at the rear but the connector is perpendular to the PCB so connects vertically. On this PSU there are a some vents on either side of the rear connector as well as at the top rear of the PSU case, plus an open gap of 4-5mm both above and below the PCB at the rear.
As you can see the aluminium surround doesn't leave much in the way of ventilation and there's not venting on the top of the case.
So will probably just pull in a standard PSU to see what's what with it. Depending on shipping cost it could be a cost effective alternative to FSP500-50FSPT, but who knows what the fan speed controller will be like. It could just be set high for server application where its not such a priority. Shall try to get one in for test.