Is the Gibertini feedhorn the same as the Raven/Channel Master one? I've tried the Channel Master one with the converted IBU and the results were worse than with a plain IBU...
That said, your feedhorn looks different from my CM one.
When I tried the feedhorns with the Invacrom single, the Raven seemed to work slightly better (you have to do a bodge to put it in the right position), although neither worked as well as the IBU single (unconverted). I believe clown man got different results. With the DIY IBU single conversion, the Gibertini definitely works better than the Raven, although I'm not sure the latter is worse than the plain IBU.
I'd be happy to get rid of the Invacrom C120 single & Raven feedhorn combo although what I'm saying here would undermine any honest attempts to sell it.
I find it hard to understand why the quad version of a LNB would work better than a single, but people do seem to find that to be the case.