According to LTA.....
If your roof top has.....

you need to switch on your meter.....once you got a passenger on
board....
Like it or not... it is a regulatory offence if you are ferrying a
passenger (even your family members) if your Meter is not switch
on.
Even if you are on Hourly disposal or AP transfers.... you need
to ON THE
METER as well. And do the necessary
(like K1+K4) or Job details button for CDG Limos.
The additional surcharges (by
TS) are add on for different calls, specify
requesting for a Limousine cab
on - (current) and/or (Advance).
It is a market practise for many years liao. As not all
passengers are willing to payFixed Prices and
as bro rbs70 has replied - the fixed prices are only "legalised
and/or recognised by LTA" is the Changi Airport
Limousine counter.