I wouldn't worry about taking them back. My mechanic recommends topguns, and fitted them to my Dad's EL. That was good enough for me, I went and put a new set on my EL along with NGK V Grove plugs and had it on the dyno. 120rwkw from an EL 6 with only a cat back exhaust. I've had them on and off a bit fitting the new plugs, and haven't had any issues with them falling apart. Dad's had his for 6-8 months now, and still going well.