The third advantage applies to the higher spenders. If you spend more than S$50,000 per annum, you will receive 20,000 bonus miles (10,000 UNI$) as an incentive. If you do not meet this criteria, paying the annual fee will not award you the bonus miles.
You may also wish to check out UOB's Mileage Calculator to estimate the number of miles you can earn in a year based on average spending.
The Bad
There are not many disadvantages that I can attribute to this card (apart from it being an AMEX). Don't get me wrong though, I'm personally a huge fan of AMEX but I know it can sometimes be exasperating because not all businesses take AMEX as a form of payment.
Casting the AMEX acceptance limitations aside, the first bad point about this card is one that I have previously mentioned - there are no bonus miles being awarded when you pay the annual fee if you do not meet the S$50,000 spend requirement. However with that being said, most of the people I know with this card do not have trouble waiving the annual fees off as long as you utilise it.
Like all other credit cards, this card isn't a one stop solution in maximising miles (unfortunately I don't think there is one). It is however a seriously strong contender if you want a card with complimentary limousine transfer service. Plus if you do spend on miscellaneous items that are generally not in the bonus earning list (with 4 miles/S$1) , this card can seriously help to fill those gaps up.