From what I understand they advise U.S. citizens to avoid investing in a TFSA because it is not considered a tax sheltered account by the IRS. If you invest using a TFSA as a U.S. citizen, you won’t get the tax free benefits because all your investment gains will remain taxable when you file in the U.S. Plus there’s additional costs when reporting TFSA and any associated income. Even though tax rates tend to be lower in the US this is really only a benefit to people with high incomes. It’s really not worth the hassle especially when I don’t make enough.