Yeah.. or 'Shark soup'.
In any case my advice would be to press hard now to get it to a standard that you're happy with and have them explain exactly how they plan to make it watertight. It is much easier to fix it now than when it's rendered. I'll bet their plan is to fill it with Silicon, which will be fine for a year or two but is probably very awkward to renew in future due to difficulty of access.
On my place they made a pigs ear of the window sills. Blocked all the drainage channels, which I foresaw.. they kept saying 'it's fine, don't worry, we'll put face drains in'. Of course that didn't work since my windows had concealed drainage and any water poured into the frame ran straight past the face drains and into the insulation.
Cost me an additional £1500 to put it right after the initial installation with an independent window contractor.
The correct original solution would have been to use under sills, not over sills.
Based on my experience, places to watch our for are:
+ Detailing around windows, doors, flat roofs or any other interruptions to an elevation
+ Verge trims as you have already spotted
+ Window drainage channels - make sure they won't be blocked
+ Reinstatement of rainwater goods, mine went back on all wonky
+ Ensuring any screws they put in the insulation have appropriate fixings into the substrate if necessary. Ensuring seal around screw with blob of silicon to prevent water ingress behind
+ Decent sealing around wastepipes, etc where they exit through the render
+ Making sure that any extensions necessary to wastepipes are done internally if possible. On mine their original plan was to use a worm-thread rubber coupling to extend waste pipes and bury it in the insulation. I convinced the plumber to extend the pipes internally, but I had to lift a few floorboards for him to do that.
One other thing which has changed since mine was done is the insulation below DPC. When mine was done this was not standard practice for fear of bridging the DPC. However I think that has changed now and best practice is to install polystyrene to some depth below ground. This'll keep your skirting boards inside nice and warm and prevent any cold spots.
There is a good guide to best practice and common shortfalls in this doc:
http://domestic.sersltd.co.uk/wp-content/uploads/BRE-White-Paper.pdf
Pretty much all of the 'mistakes' in this doc were made on my place.