The main issue with those C & Ku band combo LNBF's is the spacing between the C and Ku LNBF components is fixed so based on the F/D ratio of your dish, it can be almost impossible to adjust the focal depth of the LNBF in a way that both C and Ku band reception is maximized. Because of this, the combo LNBF design should have a way to adjust the distance between the C and Ku band LNBF components.
I know an orthomode feed is the ultimate performance solution but the cost of this makes it out of reach for most people.
I respectfully disagree. The main drawback in the present combo lnbfs is poor design. Both the chaparral bullseye feeds and the corotor II's, have no provision to adjust f/d ratio separately between C and Ku, but the efficiency does not suffer.
Also, I am running three receivers off of my corotor II with single output lnbs and splitters. The only drawback here is that all receivers must view transponders with the same polarity.