Faulty - RMA issued :-(

Wasn't happy with the performance of the ring flash I bought recently.

While it worked well with the lens wide open in ETTL mode, images were becoming increasingly dark as you stopped down. I initially thought this was simply a quirk, but, today, I did some more rigorous testing.

A controlled test using a grey chart that wouldn't affect any exposures in the camera. Tests done at different apertures and different subject distances proved that the flash was simply under exposing by a stop for every stop increase on the lens. In manual mode minimum focus distance and at f32 aperture, it exposed correctly and just as you would expect for a flash with this Guide Number.

Had to do all this to prove to myself that I hadn't messed up and missed something which is easy to do in these complex cameras that have some many different settings.
Also did some test shots using my Canon flash and that obeyed the ETTL instructions from the camera perfectly.

Called the supplier, and, having done comprehensive testing, they're happy to send a replacement once I have this unit returned on an RMA. 

The question then becomes, is the unit faulty, or, is there a generic problem with this flash when used on newer mirrorless cameras?
The flash interface hasn't changed for many years, so you would expect it to be OK. Let's hope it is just this one unit.

All a bit of a faff, but, at least I haven't done something daft. It wasn't me!