A little napkin math says the columnar mass of the Martian atmosphere is 18 g/cm^2, versus 10g / cm^2 of aluminum shielding discussed in the paper. So being on the Martian surface would probably give you something like 1/10 (atmosphere + planetary mass + environment suit) the heavy ion radiation exposure of deep space. You'd need to be pretty deep underground most of the time (no windows, at least) to be safe for the duration of a reasonable visit. I'll pass!