They're barely a 2.5" shock body, with no extension of available travel, they're rare and they're $700 a pair.
You can get 5100s with nearly the same performance capability for $350ish or spend another $300 and get full coilovers WITH springs (worth about $300) that are extended travel, and are fully rebuildable. And for another $200 ontop of that you can get those same coilovers with enormous reservoirs if you were so inclined to need that.
It's a sales ploy, plain and simple. Bilstein is trying to get into the coilover market share for stock replacement by being marginally cheaper than a high performance setup without the performance gain.