30 Block for 0 is very good! In evaluating the downside, it's important to understand what it actually means: Relics and Powers which are in play can still make Block, and the debuff ticks down at the end of the current turn, so it's only next turn that you have to worry about it. You can also prevent damage next turn by reducing enemy Strength, retaining Block, killing the enemies... lots of options.
.
