I know from experience.
"If you use it, you are trading directly with BV"
Not true. They do have bots trading for them, but not all trades are with the bots.
"they don't tell you this"
Not true. I was aware of this before using their system.
"they basically rape you"
Not true. I checked a few contracts to see whether the "P" was displayed prominently. It is. But also, there were orders which were matched partly by BV and partly by other BV users, and plenty of orders were matched below the price I bid. I can't say for sure whether I got the best possible price but if I paid less than I was willing to pay then I have no reason to complain. My usual technique was (I've not bought any in a while now) to put in a cheeky bid below all the listed offers, for a small amount of gold, and it was often immediately filled at or below that by BV.