According to a surgeon who spent many years in Singapore and only moved back last month, their system works VERY well. Hardly any recidivist crime.
They get 2 sheets and 2 shorts, undies and tshirts. That's it. They don't even get a mattress. No heating - though I assume in Singapore that isn't really a major issue. They serve the full sentence and if, after all that the re-offend, they don't get out period.
The recidivist crime is down in the single digit percentile and I tend to think the ones who go back should probably be in the mental health system anyway.