In my playthrough of classic mode I came across only 2 shields with block chance. Both of them only had a 1% chance to block.
As they are right now, and assuming they stay more-or-less the same as the game progresses, shields are not worth it. They make your attacks require 2 AP instead of the 1 AP a single-handed weapon would typically require and only give you some extra stats and physical armor. You could get the extra stats dual wielding and also increase your damage for the same amount of AP/attack.
Shields would be worth it if they gave both physical and magical armor and if they gave a good bit more than they currently do.