I like the brass molds. Prefer them to aluminum although the weight is apparent. They drop bullets nicely and hold a constant temperature while casting.

I cast with all 3 but nowhere near that temp.

I have a couple of old west molds that are brass.  They are some of the easiest molds to cast well with, and come up to temperature pretty quick.  900 is way too hot, and I think I cast about 50 degrees cooler with the brass than with steel.  I shoot antimony lead, and just where it starts to show a frosted surface is where the brass casts best.  I think more like 680 to 720 degrees.

Only problem I have had with the brass is the lead smears/solders to the top of the blocks, I have to scrape it off occasionally and re-graphite it.

Speaking of brass molds, here's a Jim McLemore-"Pope" Universal brass mold from the 1980s. I've cast with the cavity shown and find it user friendly but unfortunately it casts bullets a bit small for any of my .32cal rifles. Fortunately, the handles are being fitted by Jason Brewer with two new sets of blocks for .32 and .38cal bullets as I write this. I'll be reporting on casting with this setup in the not too distant future (hopefully  )
I've found the casting temperature sweet spot for this mold is 780˚F using 1:20 (tin:lead).