Mine is still evolving and whilst I like the current format (butt-mounted scrubber), it does come with different headaches. Learning to dive it required a lot of care, especially on ascents. The twin-format was much easier from this perspective.

I share dil between the two. Both have ADVs and BOVs.

I carry 7li dil and O2 onboard, and a small off-board O2 cylinder. If I get round to doing demanding stuff, I have room on the case for two more cylinders and could add another pair of 3li with reserve dil and O2. This would be so ridiculously heavy that it would only be useful in certain circumstances.

My BOB is currently 100% manual. I am looking at ways of making it 100% ECCR - electronics isn't the problem but where to put them in the unit is.

When fully ECCR'd up, I'll dive the BOB as the primary (bigger scrubber) and save the "proper" one for emergencies. I was on the verge of buying the Pelagian O2-add for this, but found the Shearwater setpoint controller neatly "upgraded" the BOB for normal use. That means I can leapfrog the current primary (a Classic) and get a better system when available. The Narked@90 Pursuit models looking very likely for this.

The unit case is very robust, so good for overhead stuff. It isn't perfect though and the only way to carry it easily is to wear it.

My dream is to make a small unit out of a solid block of something, with twin axial scrubbers set up for the easiest hose routing. Small, light, redundant, efficient, with every scrap of sofnalime being used and no trouble for those with glass backs. Currently, the only suitable thing seems to be a truck engine block, which would be marginally lighter than my current unit but has O2-clean issues.