I used copper for years until I called in to see my brother who was renovating his house with plastic. He used JG speed fit for virtually everything (ch and h/c) and we then had the 'friendly' discussion about 'they won't last'.....'you're mad'.....'you wouldn't get me off copper' etc etc.
When he finished (approx 12yrs ago) he gave me several boxes of unused fittings and pipe (I'm the hoarding brother) and, being the inquisitive one, I took them apart, played about with them and then used them to help me fit temporary water supplies around our place when we were render/skimming.
Long story short, and 10yrs later, I've completely renovated our place and apart from the 1st few metres of flow/return copper from the boiler EVERY pipe in the house is plastic with mostly JG fittings and others from Wunda. Along the way I did have the odd issue but this was because I tried saving a few pennies by using much cheaper fittings - these were swapped out for JGs.
The JG fittings have a satisfying 'clunk' (that you feel) to indicate the pipe has been fully inserted and then they are then further screw closed for surety. I've inadvertently forgot to screw close the odd one in the past but even then they don't tend to leak as the seal and metal collar 'bite' is sufficient anyway.
I did have a few sleepless nights prior to turning on the mains and ended up borrowing a compressor from a mate and took the pressure up to 10 bar with no issues whatsoever......slept fine since
1st plumber who came to sort out the boiler said he had switched over to plastic years before as did the plumber who fitted my ecocent cylinder.
Funnily enough I woke up to a wet kitchen floor yesterday morning and, removing the plinths, could see a fair drip dropping off the underside of one of the JG tees behind the dishwasher. Removed the DW to find that it was not that fitting at all but the screw-in ikea dishwasher fitting that had very slightly, somehow???, unwound itself causing it to drip on top of the lower JG.
I know this is only my opinion but I'm amazed/frustrated by those who condemn plastic systems when they have either not had experience of them or are copper luddites.....I used to be one but never again.