I am playing devil's advocate 

1. the dividend is quite good (so far), with a guaranteed rate of 2.5%

Good in the sense that it is guaranteed by the government (low risk). Bad if you compared to other government guaranteed funds like ASB. And if you willing to take higher risk, then there are better investment returns elsewhere (some 10+% depending on your investment acumen)

2.you're getting 6k tax relief

You can get the same 6k relief with insurance.

3. the returns are tax exempted

Returns from capital gain is also tax exempt. Dividends from stock is also 1 tier dividend which has no more tax in the hands of stock holder

4. you're getting free money from your employer (12%-16%, depending on where you work)

Look at it another way, it is the money which your employer can't pay you because they have to contribute their share to your EPF account. It is imputed in your net salary
Other negatives of EPF :

1. It is in RM, which in 2015 and 2016 has depreciated from 3.0 to 4.5 in USD terms. That is 50% depreciation which takes 8+ years of 6% dividend. In another words, 8 years of dividend gone to the drain in USD terms

2. It is money you can't use until 55 y/o. No flexibility

3. Money is lent to government and GLC. You heard the news of how they spend money ?

4. How safe is the guarantee from the government ?

5. If really EPF payout is only 2.5%, it is a bad investment. I think even 4% like FD, everybody will jump and complain. And it might happen very soon

Actually ASB not really 100% halal...
But some states says okay for Muslim to invest... As long the "sin" portfolio don't exceed certain percentage
🙏