Being that 1 Evasion is +.5% chance to evade, these give you an additional 7.5% evasion, as long as you're not capped.
Kind of a catch-22, though. Only useful when you're in the red, but anything that can knock you down that low is likely to kill you....
Not to mention you can even get away with blinktanking since some TP moves can ignore shadows.