Pros
They have a lot of ill-gained money, and might pay you well.
Cons
They didn't earn that money. The caseload is impossible, and makes the firm seem like a pyramid scheme. They treat very individualized petitions (EB-2 NIW and EB-1A) like assembly-line H-1Bs, and charge unconscionable fees that often amount to more than a year's income for middle-class Brazilians. You will immediately be faced with a demand for ethical compromise. They aren't even difficult issues. To keep your job, HW expects you to behave in clearly unethical manners, signing off on cookie-cutter petitions that are unapprovable on their face. This is all to fund expensive trashy bling for the dorky arriviste at the top, who has been dinged for unauthorized practice of law who knows how many times now. If you have any conscience, it will twinge in a bad way when you realize he is selling impossible dreams to his compatriots in exchange for fees that are unconscionable by industry standards. Just walk away. H-W is toxic on your resume, you run a strong chance of professional discipline for what they demand of you, and you won't gain any useful experience as a rubber stamp.