firefly flies out of SIN via Seletar and Arrives in Subang Airport in KL. If one is heading to KL Bintang area, suggest to fly Air Asia to KLIA 2 then travel by train to KL Sentral and then via Grab to Bintang area. KLIA express train is very clean and convenient.
If one has options, perhaps can consider staying around KL Sentral such as Le Meridien / Hilton / Aloft / Ascott etc which is right by KL Sentral. Traveling by train/MonoRail/LRT to various shopping malls is easy from there.
bro, thanks for the advice/info,
of cos I'm not kumgong until book tio different flight that fly from Seletar Airport n don't land in KLIA!
it was a codeshare flight FY7322 i was trying to find out what other difference there are since it's the same plane as MH604.
so being cheaper by ard 30bucks, will kena some inconvenience of cannot do web check in from msia airline website. by right firefly flight can use their own website to web check in but their t&c got state Codeshare flight cannot use.
And then i tried to call Firefly sg hotline to try to find out more, end up the number no longer in use!

but just to share what i found out these 2 days, the codeshare flight is can book lah, will end up on the same MH flight, just that cannot web check in, and then online info will scare you and say wait till go airport then check in might have possibility of being bump off the flight. etc etc.