My parents got their green cards as direct beneficiaries of a US Citizen. I enlisted Khanna's office even though I am competent enough to do research and fill the required forms - this is because of a slightly unusual situation that I didn't want to risk. Their office does this for a living, and they know how best to address situations, RFEs, etc. They were diligent in the paperwork, the follow-up and communication.
I also knew that I could rely on their office's expertise in case of an RFE, or an appeal, etc..