One species that matters: M. balfouri, from Socotra, and it is one of the more interesting animals in the hobby for reasons beyond looks.
They are communal. Genuinely, reliably communal, with siblings raised together showing tolerance and even apparent prey sharing rather than the usual eventual cannibalism. That is rare enough in tarantulas to be worth the price of admission by itself. Blue-grey legs, tan carapace, old world temperament, so fast and defensive when handled.
Socotra is closed to collection, so every animal in the trade descends from a small founder population imported before the door shut. Prices were once extreme. Consistent captive breeding has brought them down hard, and the communal setups mean sellers often list groups rather than singles, which distorts per-animal price comparisons if you are not reading carefully.