I ended up opening a new UOB ONE account to tie back to the MightyFX card. As far as I know, the reason being I don't need to maintain any balance in the foreign currency accounts, just make sure I meet the min. balance on the main account. Even though the money has been converted into foreign currency, it still forms part of your balance in the main account.
As they issue you a debit card, there is no credit card fees imposed by the bank on overseas transactions made in that currency. However, if the merchant applies the fees then its beyond the bank's control. Debit card is free for 1st 3yrs, subsequently waived when a minimum of 12 Mastercard transactions are performed in a year. Overseas ATM withdrawal at SG$5 if from UOB ATMs or equivalent in the currency of the overseas ATM.
I only intent to use the account for overseas spending and not for FX investing purposes so looking at money changer rate vs MightyFX, MightyFX is slightly better and you can set alarm if it reaches your targetted conversion rate so you are always in control. Taking into account the additional SG$5 for cash withdrawal at overseas ATM, it only would make sense if you withdraw about $500 or more so I'ld stick to online and debit card transactions at PoS terminals.