Small negative, before the massive positives: the communication online was not great. For reasons that aren't clear, it's possible to pay in advance for training, through PayPal, in such a way that Yokkao received my money but not confirmation of payment, so when I arrived they had not scheduled my session and I could no longer meet with the trainer I had requested. It looked like I had to bail entirely on my only training of my short time in Bangkok while still being out money spent.
However, it ended up being one of the best training sessions I had in the country. The manager recruited another fighter, Iquezang Kor Rungthanakeat, to work with me for an hour. They slashed the cost and put the rest of my balance into store credit (to avoid the cost of changing back to USD). Iquezang is a beast of a fighter, but he's also a truly wonderful teacher, as good as any I've met in NYC or Boston, despite having the worst English of anyone I met in gyms in Thailand. He was funny, patient, and creative. He didn't flatter me for anything I did well, just used it as a jumping off point to go deeper into technique building on my weak points. Iquezang kindly gave me extra time on the questions I had, while also noticing the difference between my needing a physical break and when I needed a mental break. Everyone else there was generous and professional, and the facilities were top notch quality.
Yokkao may not be inexpensive (or in an inexpensive neighborhood), but it is an amazing place to spend an afternoon learning.