Still all-eggs-in-one-basket rather than redundancy - but multiple would carry weight penalties and temptation of making them less crash-survivable and risking all of them not surviving, tradeoff as always.
But with what you say, is there a reason the ULBs have to be separate and "attached" (or detachable...), why not integrated?
I have vague idea this may be to do with ULBs having to be regularly replaced as the batteries die, but these days with solid state memory and near-field wireless power and data interfaces is it now possible to do ULB / CSMU in a single easily replaceable module?