Commenting here since this is somewhat related to the research (1) I have been doing lately:

UMA is one transparency layer.

The bigger one is the public WebSocket feed itself, which broadcasts post-match book state but hides taker identity. So trade direction inferred from the feed only hits 59% sign agreement vs on-chain ground truth.. that breaks six standard microstructure measures (effective spread, Kyle's lambda, Amihud, etc.) on most top-100 markets.

I believe any Polymarket research that depends on direction should to source it from on-chain OrderFilled events, not the feed.