Dierre is a really good quality door with, in addition to the lock frame bolts and yes it is correct that the front door isn´t the normal entrance point. Unfortunately the developer can fit a variety of locks to this type of door from a full security version to a simple barrell and, if you don´t know what you are doing these can be difficult to change
Rule one is you should always change the locks after your snagging is completed because your keys have been in so many hands pls it´s normally 6 months to a year before they may decide to use the keys that that have collected
It is correct that they don´t normally com in via the front door, unless they already have the key and security is all about common sense so look at areas that can ne accessed via the roof space, for example patio doors on the bedrooms, especially the sliding type which, without additional locks. can easily be forced open