Reach to Teach - my experience a decade ago with them was positive (they placed me at Kojen which was not great but fine for a year, my complaints about that year are about Kojen, not Reach to Teach), and I recommended them to my sister. They were ok as far as she was concerned, but she ended up not taking any of the contracts they offered her because every single one had a red flag in the contract: 20k deposit, Christmas absolutely never off (which she feels is indicative of a broader cultural disrespect for foreigners), wages garnished toward a deposit that is only returned when you complete the contract, weird fines, unpaid work beyond prepping and grading etc. or just very low pay. Her complaint was mostly that the contracts offered were crap, not that R2T itself was rude or problematic. To some extent contracts in Taiwan are crap generally, but the ones she was offered were worse than usual.
Bryan Wu - I haven't had direct experience but a friend of mine who is ethnically Asian was told by him that he wasn't willing to work with ABCs or foreigners who look Asian, and that was "his choice" because "employers want people who look foreign". This is actually illegal in Taiwan. The jobs he has on offer are kind of crap too - the usual weird hours, part-time, "work permit offered" is supposed to be some great benefit when it's really just a legal requirement, 600/hour, unpopular locations.
My sister also showed me some emails from him when she was looking for a job and he was rude and unhelpful (and the jobs were also crap - 540/hour to work in Sanxia! Woo!). She had told him she specifically wanted to work in Taipei and he was all well I think you should consider Taoyuan / Here's a job in Kaohsiung, you won't do better than this, you should just take it / "This is a job in Linkou" "I don't want to live or work in Linkou, I said TAIPEI" "It's close enough you should just take it, you won't get a better job"...and when she wrote to him to ask him to ONLY send her job openings in Taipei or inner ring suburbs - Yonghe OK, Linkou no - he was all "Well there's no solution then, you aren't going to find a job in Taipei."
She blocked him from writing to her as he was unhelpful and pushy (really? NO jobs in Taipei at all? Uh huh) right before finding a job advertised by the school directly...in Taipei.
Sandra King - she pops up on Facebook groups often and people say she herself is professional and handles placement and paperwork well. However, there have been complaints about the schools she works with, and her default (as seen by many of us on Facebook) is to defend the school and slag off the complainer ("the room wasn't dirty, just rusty and a little old! Sure there were mosquitos but you can get a net!" "You're probably lying about the neighbors talking loudly, maybe you talk to yourself unconsciously and that's what you heard!") which to me is a big red flag.