Don't want to put the dampners on things mate but that sounds very much like a typical sales pitch you have been given and it was only recently that a report came out about inflated new house prices due to these so called sweetners. If I find it I will post it but some lenders have just upped the deposit required by some peeps (mainly buy to let) buying off plan as the true value of the home is actually a lot less in real terms due to discounts etc.
Be very careful as it may be the case that when you move in you will have paid the actual market rate and will not see any discount at all.
It sounds a bit mean of me but just be careful as the market is very weak for new homes, there are 25 new luxury appartments going up near me and a number were sold off plan in the first few days but weeks later thay still can't shift the rest and have dropped the price 3 times already!!