Positive - more awareness and access for large pools of money.

Negative - they are selling paper bitcoin, not the real UTXO. Meaning the price of bitcoin in dollars can stay artificially lower because you are “inflating” bitcoin by having fake bitcoin in circulation.

This is what FTX did, Sam sold 3 billion paper bitcoin to the public but he didn’t have any real UTXO’s on the balance sheet so when the public came for their bitcoin they didn’t have it.

Blackrock can choose to be better then FTX and hold actual UTXO’s on the balance sheet, but I doubt it.