I'll say it may be O 405 NH, Citaro, Citaro G, all of which are
stepless models.
They buy only a few units probably because they not rich enough to
buy more !?! [Unlike in oil-rich Saudi Arabia say where they buy
real original M-B O 404 coaches by the hundreds & go to Germany
for handshake handover ceremony & tour the Mannheim coach plant
before collecting the vehicles ! Similar to buying an SL 600
convertible & getting that sort of service]
But i'll prefer to believe that they only buy a few because they
are more prone to buy Volvo nowadays since they are the Volvo truck
& bus distributor here & just want some comparison &
'competition' in their fleet so as to see how their preferred Volvo
would perform in the long run versus the other makes & models.
Maybe also to show Volvo that they still use other makes hoping
that Volvo might give them better deals when they want to buy Volvo
in larger quantities ?!
Also another noteworthy point i'll say is that no matter how good
they think their Volvo might be, it's always wise to have some of
the other makes in the fleet as well as putting all eggs into 1
basket is not always that wise !
What happens if 1 day Volvo goes into difficulthy say on strike
etc. & spare parts supply is disrupted then it's always good to
have some other make around to depend on ! Not likely every make
would go on strike the same time !