Im very new to plumbing and am only self taught so my advice is only from my own experience. Speed fit is as it says and it makes the job much quicker it is designed for heating aswell as domestic water i use both copper and speedfit it all depends on the job at hand. as long as he is using the pipe inserts which stiffen the ends of the plastic and also create a secondary seal then you should have no problems.
John Guest - The World Leader in Push-in Fittings, Pipe and Plastic Plumbing Systems
this should put your mind at ease.
Good luck..
Mat