Are there any disadvantages or penalties for clearing HDB loan fast? (Eg 5yrs)?

There is no disadvantage and no penalties.

The only disadvantage is that the amount you use to clear your HDB loan, for some people, can be used to invest elsewhere and earn a higher return than your loan's interest rate.

No penalties. The "disadvantage" is that you are locking your money into your flat very quickly when you could have drawn more value out of it via investments and/or top-ups to CPF SA.

The advantage will be a peace of mind.

Before you clear your loan quickly, please verify that you will not have any other more expensive loans in the near future (e.g. credit card loan, car loan, personal loan, etc).

Also, when your loan is still ongoing, always ensure you have at least x months (where x is usually 6) of monthly instalments ready in your bank account or CPF.