What's the difference between these 3 HDB options?

Just for sharing.

I loan max in 1996 about $200,000 for my second HDB even after I get my $180,000 profit from my first HDB when I don't know what to do with money.

Fast forward, now I have 2 condo and a HDB officially.

When you don't have the cash and opportunity happen, you lost the opportunity. ​​​

1) Reduces your liability and future interest owed.

2) Reduces future accrued interest and allows your unused OA to grow at 2.5% interest.

3) Reduces existing accrued interest and also allows refunded OA to grow at 2.5% interest.

My take is that accrued interest isn't too bad. In fact it becomes a Bank account of sorts in the future to get guaranteed 2.5% whenever you want.

But if I have extra cash now and I'm confident in making more than 2.6% in compounded annual returns, I'd just invest the cash and continue paying my mortgage as is.

But if I'm not too confident in investments, I'll do number 1 so I reduce interest payments and clear my liability faster.