I've worked with marmosets and tamarins for years. Having worked with them, I would never own one. First of all they should be housed in pairs, nothing less. They are social living animals and should not be kept isolated. They are not even remotely clean and have a fairly strong smell. Sure they are cute, but they aren't good pets. I loved it when they would reach out and grab me or groom my hair... until I realized they had just had poop in their hand or had been picking at their genitals. They require a lot of care, especially mental stimulation and meal preparation, and ideally lots of space. Many places also require permits to have them.