Bottom Line folks is Plastic is fine. REMEMBER installation procedure is key. So.... Rough burred copper tube edges (quick job = low cost), and flux and hacksaw cuts is bad news. For pro's, you know what I mean - hopefully: for the 'public' members of this forum, please note that if any work you do, or subsequent 'professionals' do, any flux that runs down the line and gets to any of the plastic O ring seals (I am a huge fan of Speedfit - where's my commission???), regardless of manufacture (JG Speedfit; Hep2O: Polyplumb etc..), will likely as not, destroy the sealing ring and may cause a leak!! Rough tube ends, cut incorrectly is a nono! Install correctly (just like copper correct install is vital), the correct install is crucial - don't cut corners. If you want an el-cheapo job that sees plastic as time saving/cost cutting easy route - then you will come unstuck. If tubework is visible, I still tend to use copper for aesthetic reasons, but there are times and reasons when end feed (solder) is more appropriate, as indeed there are times/ reasons when compression is better as indeed there are times / reasons when plastic is better / fine. Time moves on and technology and the world finds better ways of doing things. I fly in a jet or turbo prop, not a propeller biplane: I don't keep harking back to the past but accept progress.