What does it mean if I use a reliable broker but it is not regulated in Singapore?

Hmm, perhaps you could share with us the broker that you are using/intending to use? I think such things are quite dependent on the individual brokers themselves.

But generally, non-regulated brokers are seen to be more risky as they have not been subject to the regulations of MAS. As such, some of their practices may be questionable or they could just be fraudulent comapnies even.

Which brings about the question, why not just use a regulated broker?

If you're not sure which one to choose, you can check out my comparison here!