Fix comparison tool by asking for blocks more aggressively

Rebased-from: b33b9a6fefbe832bf45a6c7717d0537f27597bff
Fix uninitialized variable added in b33b9a6fe

After discussing with BlueMatt, this appears to be harmless in its
current state since it's always set before it's used. Initialize it
anyway for readability and future safety.

Rebased-from: 106f133de6bdb577c4135847fd703d08f525ba46