What part of Brooklyn is he considering? How much of a mortgage he wants to carry would be something to discuss with his accountant because he needs to decide how important the tax advantage of being able to deduct the interest is. If, however, his goal is lower monthly payments, he could achieve that and know that his investment of the large downpayment is a very solid investment. He should weigh that investment against the likely return on other investments. Also the time frame he plans to stay in the condo would be a factor. I live in the Slope, so if you'd like more specific info about buying in this or surrounding neighborhoods I'd be happy to answer any specific questions.