Thoughts on Shields Shall be Splintered

The original is at Trollsmyth's page here. It's a wonderful rule and I've incorporated it into LotFP games in the past. I wrote a previous post about shields and armor, with different shield sizes and materials. Wood can be sacrificed once, metal can be sacrificed twice. I am thinking about changing that though. Both can be sacrificed once, but metal shields give a bonus of +2 melee AC and +2