Zero
Master Black Belt
It's a matter of cost, international schools charge several times the fees of local government schools, however, if OP's expat package includes for his children's education at international schools, then I'd say it's definitely worth serious consideration.
On a side note, I don't think the Singapore education system is more pressurizing than the PRC system. Maybe that Chinese family's kids found it particularly difficult because the medium of instruction was in English?
Am not sure how long we would be there but taking things all the way, would you know if, for example, kids did well at international school, and not local school system, they could still equally access top Singapore universities? Or would they be disadvantaged obtaining admission to uni with respect to kids in local school system?