"I replaced my bathroom tap a few weeks ago. The new tap hoses were a little too short so I had to extend from the isolator valves using a few inches of extra copper pipe. These olives made a nice water-tight job. Still no leaks, fingers crossed. Nice and cheap; can't really see why you'd need to pay more. But then, I'm no expert."
"These are 15mm olives. To be used externally and not to be eaten. They are round and fit very well round 15mm pipe. When squashed in compression fittings they provide a waterproof seal. If you are hamfisted when tightening them up they are prone to leaking. Do NOT overtighten. [ If a small leak develops they can be tightened up a little more - they cannot be untightened if you use too much force.]"