My experience suggests legit.
No locks or bolts on doors
No sign of wet wipes or clean up materials
The lady who I saw was "helping out" and usually works in Royal Thai (Fishponds) which, as far as I know, is legit too.
Nothing in the conversation to suggest anything else would be on offer.
Towel remained on throughout.
She "took my breath away" ... in terms of "ouch ... that hurts" rather then "hmmm ... that's nice".
Towel was held up as a shield during turnover
Massage got nowhere near top of thighs.
So there were too many legit messages to consider embarrassing myself by asking her if anything else was on offer.
YMMV