The social velvet spiders, and one of the few genuinely communal spiders on earth: colonies of hundreds share a single silk fortress, hunt cooperatively, and raise young collectively, with mothers ultimately feeding themselves to the brood. Nothing else in the catalogue does anything like it.
A colony is the product. The keeping is a silk city in a well-ventilated enclosure: dry, structured, anchored, and fed as a group, with the web growing into architecture over months. Individual spiders are small and short-lived; the colony persists and is the animal you are actually keeping.
Venom is unremarkable. Supply is thin and irregular, since colonies ship poorly and few breeders work with them, so availability arrives in rare pulses and prices form on scarcity of functioning groups rather than of spiders. When a colony listing appears, it rarely lasts long.