The local insurers's health insurance plans are generally much cheaper but are not as comprehensive.
List of exclusions:
Pregnancy costs(except in the case of pregnancy complications)
Outpatient Care which does not lead to hospitalization
Non-emergency costs that does not lead to hospitalization.
Normal medical costs such as flu, fever etc
Note that, in most of the cases, a claim can only be done if one were to be hospitalized, while certain day surgery can be claimed too.
That being said, local insurer's health insurance still provides sufficient medical coverage if one were to be hospitalized or being diagnosed with criticall illnesses, at a affordable cost.
Do note that among the five major insurance companies: Great Eastern, AIA, Prudential , NTUC and Aviva, there are certain variations as well.