Yes legal fees and stamp duty is the same as buying a subsale property.
And probably legal fees will be slight lower coz no need to do S&P. Just Deed of Assignment.

Risk:
1. Cannot check or know inside condition of the unit.
2. Possible double transfer if individual or strata title already issued by the developer but perfection not done. Developer disagree to direct transfer to you. 
3. Hard to get loan if you buy a property that is more than 10 years still under master title. Example: Lagoon Perdana, Flora Damansara, etc.
and many more actually. Case by case basis.

Title is perfected and the title is clean, will be the most ideal situation coz name transfer will no longer depend on the developer (or liquidator if developer bankrupt)
Cash in hand:
10% as downpayment, balance 90% from bank loan (for your 1st & 2nd property)
5% as legal fees, stamp duty, valuation fees (some bank allow this to be partially included into the loan)

Once individual title or strata title is issued by the developer to the owner, you must appoint lawyer to help to transfer the title to your name and also pay the stamp duty MOT cost.
Majority lelong unit owner got no money to pay because the cost is not cheap.
So the process is incomplete, hence the term perfection not done or not completed yet.

In order to buy such "hanging" incomplete title property, must depend on the developer whether they allow direct transfer to your name straight. Some developer allow free of charge. Some developer allow but you must pay them certain "admin fees" but it is still worth it compare to double transfer process.

If developer disallow direct transfer, then you need to "help" the default owner complete the perfection process first. Pay the legal fees and MOT for the default owner. Once completed, then only you do another name transfer to your name, paying another time the legal fees and MOT. This is known as double transfer.