But yeah I don't think people realize how strong stun is. I remember Doom_KUTT and his +3 bar mace (5.0 weight) terrorizing siege, I swear over 50% of my shield blocks got me stunned.
The +3 bar mace is a very popular weapon now, and the block stun is what makes it so effective (although high damage and knockdown don't hurt). All 1-slot shields and all weapons will be frequently stunned when blocking a held attack from a loomed bar mace, allowing a free followup swing for the bar mace user. Often this followup isn't blocked, because the stunee doesn't realize they are stunned and tries to attack anyway.
The 3kg SoW isn't on the same level as the bar mace, but it can still stun Elite Cavalry shields and lighter, all 1h weapons, and most 2h/pole weapons on held attacks. You just need to recognize when you deliver a block stun, then attack a second time in sequence for a "free" hit.
High weapon weight is very good, with virtually no drawbacks.