I have done this route 5 times in each direction. In my experience the main risk is that the flight is late into SIN, in which case you have very little time to use the lounge before returning to the gate, especially as the terminal is so big that it can take a while to get to it. Also, if you're travelling with hand baggage only and have 2 or more items, be careful with security when back at the gate. The security zone is quite cramped and, if they decide to be throrough, the process can be a bit of a pain.