Just to put in a bit of balance, I got a set of leads from powerspark, allegedly for a rover V8, however the lengths were different from the ones I took off some a bit shorter others much longer, they did look them part, but on changing the plugs a couple of months down the line 3 of them fell to bits.
Contacted powerspark and they said I removed them from the plug incorrectly, and caused the leads to fail, hence no replacement, after 20 years in the motor trade I kinda know how to take a plug lead off
Replaced with a set of champion leads which have been off for servicing without issue, I potentially had a one off bad set, but if I was buying expensive leads again they would be magnecor