I live in US and from Thailand. Grab in Thailand is much worse than Uber/Lyft in US in terms of experience. The fundamentals don't work well. I used Grab 5 times in Bangkok and only succeeded once (e.g. the driver accepted but never came, the driver almost arrived but turned away). In the success case, I waited 20+ mins (which is normal for Bangkok's traffic, I guess). In US, the reliability has been 100% for me, and the wait time is like 10 mins max.