I've stayed at the Fragrance Emerald in Geylang several times. The 'short time' trade is kept on different floors from the 'standard' tourists, you will occasionally share the lift with a young woman in an outfit rather OTT for daytime, and an older man with a big grin on his face, and they will go in different directions when leaving the hotel - but the area does not feel at all unsafe, just keep the usual eye on your possessions on the street although I've never had any trouble. Plus Geylang has loads of excellent food opportunities at prices a fraction of what you pay in the centre.
The hotel is a little 'tired' but everything is clean and works, it is quiet despite being just off the main road, checkout at 12am and they store luggage. Changi 20 mins.
15 minutes on the bus to the centre, about the same on the MRT plus the walk of 9 mins to the station. Not what I call 'far out'.

