Canon user here
have and use the 420EX and Metz 48AF
Looking for a shallow diffuser (NOT the OmniBounce type) so that the light only goes to front, albeit diffused (and not to the sides).
Buy and butcher a few cheap omni's ones on eBay, by cutting em up and bringing the front backwards to close to the glass of the flash
Block off the sides with black (?) tape, so the light only goes to the fornt
I see that there are shallow diffusers (fi for the 600RT) but not fo all speedlight