22/38 barriers this is better in terms of just strength efficiency than BlacKat. It's usually more efficient than BlacKat at taking down 3 or less strength ice due to them having a low amount of subroutines (except for ice such as Hive). For 6-7 strength ice, even considering the +4 strength for a total of 7 strength will overlap by 1 on the 6 strength ice, it is still better.
Now for subroutine breaking. I think the consensus is that stealth credits are worth more than 1 normal credit. Around 2-3 credits is what people usually say, but there are times where stealth would have not been used for the turn anyway and they would have just been useless, so that's something to consider in their value. After looking and trying to calculate which is more efficient at subroutine breaking, I gave up almost immediately and just reached the conclusion that it depends and it's a much of a muchness. They are both good and both are competitive with each other, which is great. There are always going to be scenarios where one is more efficient than the other. Although, it is worth nothing that BlacKat is more efficient relatively speaking than Blackstone when breaking ice at 4-5 strength and also weaker ice where they have quite a few subroutines, like Hive as I said earlier. On the other hand, Blackstone is better at almost everything else. Blackstone also keeps it strength for the remainder of the run. And on top of that, Blackstone also only requires 1-2 stealth credits max where BlacKat usually requires a lot more. That is an extremely important thing to consider.
I think the people saying how inefficient and bad this card is are just looking at it from a Corroder and Cerberus "Lady" H1 point of view, and not from a stealth or BlacKat point of view. Blackstone is a great stealth barrier breaker in it's own right. I think this has no competition in any shaper stealth deck, as it is in faction and there's no need to pay a hefty 3 influence for BlacKat like before. That can free up room for many things such as Datasucker to make Blackstone be able to efficiently destroy any of the strongest ice barriers or even the weaker 4-5 strength barriers without having to spend money for strength, or you can add extra things like Silencer, Dyson Mem Chip or whatever your heart desires. That influence is really important and powerful for stealth especially.
I´m running Corroder in my stealth deck. Blackstone just isn´t worth it. Stealth creds are supposed to be stronger than normal creds but harder to get. Corroder usually gets me in with about the same efficiency as Blackstone (the 1:1 str boost makes it more flexible and given the lack of glaciers in the current meta the strenght boost lasting the whole run isn´t needed), so that I can use my other stealth creds to boost a killer by 2 str with 1 stealth cred+bypass sentries or a decoder+sometimes fracter by 3 str for 1 stealth (aka Penrose because markdown just brokey now)— m.p