Actually I'm amaze with the action they do since this shows that they really have huge confidence that bitcoin would perform more better in future.
But what's really bothering there is if they accumulate a lot more volume then there's really huge chance that in future also they could able to manipulate the price of bitcoin since their company might have more bigger holdings compare to other institutions. So hopefully we see positive things to happen more for bitcoin since if Blackrock will start to dump their bitcoin then maybe this will create a huge damage on the market.
To be more accurate, what they have is huge confidence that there will be ETF demand for BTC (not actually that BTC will perform well). Having said that, yes they have also said they have a strong belief in the future performance of BTC. But again, remember, they don't make money from BTC rising, as they only hold the BTC of others as ETF managers.
I challenge you to tell me how could they could possibly manipulate BTC price with their ETF? If you understand how ETF's work and the SEC law they need to comply with, you would realize that this is not possible.