"I have fitted hundreds of these and they do the job perfectly. Just fit them properly. Socket them fully, paste the olive with screwfix's own blue liquid PTFE and tighten. You DON'T need to PTFE tape the thread; that is not where the seal is made.
"These fittings allow you to join 2 pieces of pipe together while making a 90deg turn - hope that's not too technical. They don't make a song and dance about what they do but they are reliable and easy to use."
"These compression elbows are great quality at a great price. As a time served plumber I've fitted many of these and I've never had one fail on me yet. If your looking for a compression elbow these won't let you down. I don't see any sense in paying more for other brands when these are up to British Standard and do the job well. I highly recommend them."