H3 eats up your time, PSC does not consider it for scholarship.
If you take the external modules, be prepared to slog with the
extra workload where it means travelling to NUS/NTU/SMU for up to 3
times a week for lectures (usually until 6.30 pm) as well as
tutorial and lab sessions (up to times like 9pm). Those were the
times I suffered when I took the NUS H3. Travelling from Bishan to
Bouna Vista then back to Sengkang ain't no joke. Anyway, most
people pon the lectures anyway cos got webcast.
For MOE H3, be prepared to study extra for A levels since external
modules end when the grads take the exams for that module but MOE
H3 ends only at A levels.