There's no difference. There used to be a slight difference, I think one differenct ester, but now it's the usual Sustenon blend.
Whoever told you Omna's aren't good for cutting has little understanding of AAS. Not only are Omna's and Sustenon interchangable, but even if you had the older blend it would be fine to use.
On top of that they are both test. All tests are EXACTLY THE SAME. The only difference would be the release time of the esters, which at the end of the day really isn't going to make that much of a difference. So all tests are equally as good or not for cutting and bulking.