There better be something good in the chest to compensate for the rarity, but saying that, I've had more Raptor pieces than I have Trisk pieces, and look what you get from the Trisk wall...
Unslain Bosses - Clan
The keyparts being the rate they are makes sense if they ensure the chest loot is very good..
The weapons though, I don't understand the massive rarity. Hopefully we can break them down for unique perks from inventor, otherwise it seems like overkill. But if they're designed with inventor in mind, then well, I think I can applaud Jagex slightly.
Debating on whether to use them for Premier Club or not... But Premier Club and Rare Items on the same weekend is going to make them skyrocket.
Unslain Bosses - Clan