Andy, while I understand and support your thirst knowledge and understanding of scrubber designs there are but few people that can impart it. Else we all would have excellent scrubber designs.
More importantly is probably the question "does it really matter?"
The pros and cons of the two opposite flow directions have been pointed out pretty well I think. The PRISM has them. The Hammerhead has them. Either way I'm sure you're getting one of the more capable canisters out there, with a lot of absorbing capacity. One has around 6 lbs capacity, the other 7.5 lbs. Which one would be more efficient had they the same capacity might be of intellectual interest, but IMHO doesn't matter as they don't.
More important is their duration, rather than how they got there. For the PRISM that's fairly well known as SMI has released some testing data, though more is needed I believe. At CE standards for one thing, to be able to a fair comparison, and for more than 60 ft at that.
The Golem scrubber is being tested as Jakub posted, and I hope those tests are done to the general CE protocol, with data for 40 m (plenty of comparable data thanks to Kevin Gurr) and 100 m (available for Inspo, Evo and Ouroboros).
The same, really, goes for just about everything else. For an exploration level rebreather flood tolerance or ability to drain the loop are good features to have, even a small, slow leak can add up if you have 5, 8, 10 hrs of deco to worry about.
You look at the rig, you look at the features, and you choose what suits you.
Anyone with an Optima watching you pack your scrubber with the factory recommended Sodasorb will probably say "No friggin' way". You'll take one look at them changing batteries on their secondaries and say the same.
I have no problem with the Hammerhead's scrubber, other than that it's way bigger than what I need. The cell placement issue is different though, I doubt I could get comfortable with that. But that's just me, couple o'hundred Meg divers don't seem to be bothered by it. Same as the lack of an independent pO2 gauge on the AP units. It's a problem for me, several thousand owners don't have it ... shame really, John and Beanie should get rich fixing it.
