Everyone says these plans defer taxes. This is only half of the truth. They defer the tax and the tax calculation. They only make sense if you know that you will be in a lower tax bracket when you take distributions.
Given the history of income tax rates since 1913, is there any way for you to know what your tax rate will be when you begin retirement? Would it make sense to diversify your tax rate risk by putting some of your retirement funds in an after-tax account?