It is almost a must if you're a casual player. It is too hard to keep up with the barters, flea market rates and even just the quests and items for quests.
Yep. :) I signed up a couple months ago for historical market data because I'm a sucker for that, but the added features since then have really cemented it as a good decision.
I haven't played in a few weeks though, from a combination of the friend I usually play with being less interested (and not wanting to level/quest much without him) and being busier myself. That's sad, because it really is pretty amazing once you get the hang of it (I just stared at beginning of this wipe) and have someone to play with. Playing alone is fun too, but with one or two good friends is really something special.
AFAIK he's using RatScanner[1], or something like it. I'm pretty sure the admin of RatScanner is in the Discord quite a bit, but that could be a coincidence (but I think it's some form of image processing lib no matter what, they include a screen cap of the latest market info for an item on the page when you pay).
I'm not sure I would consider what they do effective in banning trade bots (the captcha seems ridiculously easily beaten), I think the Found In Raid object flag is probably the really effective thing keeping most bot usage down, since it attacks the actual incentives of using a bot (it's still useful to auto-buy when markets dip or someone under lists an item, but that's about it I think, but I may be missing a use).
That said, if all you're doing is scanning the market results and not buying anything, it's probably much easier to not trigger any problems with the devs. The market data is really useful for those that like that sort of thing, but it's not really that much of an advantage, just a way for those into the economic portion of the game to go deeper.
It’s all done just by image processing. Once premium you can see the screenshots of the items on market used to provide the price estimate. They must have a couple accounts running continually going through the market checking prices. That’s why some items are 2-3 hours delayed.
It is almost a must if you're a casual player. It is too hard to keep up with the barters, flea market rates and even just the quests and items for quests.