Roof shingles are thicker than shed felt, stronger and longer lasting. IKO tests the tensile properties of all its roof shingles for tearing so when you consider some of the
cheaper shed felts which will rip like paper there is no comparison. You should also consider that the average life expectancy of shed felt is 3 - 5 years whereas with roof shingles you are looking at 10 years plus (depending on external factors)