If it ain't leaking, don't fix it. Asking a ham-fisted installer to mess with the pipes is asking for trouble.
Well, it is!
(just to add some sparkle to the party)
I much prefer soldered fittings (kinda bullet-proof really) and compression fittings after that (at least you can nip them up tighter if weeping or take them off and re-do if necessary).
I'm not a fan of these push-fittings at all. If they weep once fitted, there's bugger all you can do. Even the Pegler Tectite are susceptible to weeping - trust me, I know - and these are supposed to be the dog's ********. Fitted one of these to a 15mm pipe for an external tap. Was put on square and solidly pushed home and it wept. Nothing else I could do. Had to angle grind that bugger off - so not a fan.
That said, push-fit waste seems to work okay prividing you get the correct pipe to go with the fittings (another hard lesson learned).
XRD