Dr Tan was my gynae for 2 kids, so I clearly thought highly of him. I'm in a family of doctors, so the primary consideration was whether medical outcomes would be good (rather than things like do you get photos, what are the package rates, etc.). On this criterion, Dr Tan is universally known within the medical circles as being the best: complex cases across the island get sent to him, and if C-sections are needed he completes them in 15 mins (very fast) - which means very low complication rates and better outcomes for both mother and baby. All doctors can deliver a baby when things are straightforward, but Dr Tan can calmly manage a situation when complications arise - so he is the clear choice for many many doctors' babies.
That said, I've recommended him to a few friends outside the medical circle and they switched for their second kids. They felt that childbirth was special, and that SGH didn't give the "frills" - eg they wanted to cut the umbilical cord and it wasn't automatically offered to them. So Prof Tan won't work for everyone - it depends on whether you weight medical outcomes or customer service more.