I read a thread somewhere about how a combo LNB wasn't as good as stand alone LNB's.
Other than on a BUD how can 2 LNB's work on a motorized dish?
"Combo LNB" ?
Not sure what you are referring to, but Invacom makes a Ku band dual-mode QPH-031 that does linear Standard, plus Circular, all in one.
I don't think anyone has had any negative comments about it, other than high cost and heavy weight.
Otherwise, most reports tend toward happy users.
As for mounting two LNBs on your Ku dish, the above comments and many threads on the forum support that approach.
For C-band or BUD dishes, there are dual-band LNBs.
Some have reported variable success with them, but I believe the latest tests by Linuxman have uncovered some of the ways to make 'em sing.
There are some commercial C-band scalers with Ku-band LNBs mounted on/in them beside the traditional low-band feedhorns, as well.
And, some users have bolted/tie-wrapped Ku LNBs to LNB support struts to get more FTA.
What was it in particular that you had in mind?