Be afraid, Be very Afraid!
There is nothing wrong with being risk adverse.
The question to ask the housebuilder is WHY can't I have my own professional inspect my house before legal completion? It is soon to become a legal right, but as I understand it is not at the present time.
My guess is there are worried the inspector will find hundreds of snags, defects maybe even something serious and expensive to put right, all of which they don't want you knowing about until after they have all of your money. Then, they can fudge, delay and deny and make you fight to get your quality new home rectified to the standard you thought you were buying.
In addition, buying the last house on a site is bad because all of the trades and site manager will be gone very soon after you move in and you will be forced to deal with the regional office who always seem to find it mostly beyond them to arrange for trades to come back to fix issues when they say they will. You will also be paying top dollar for it!