I have seen fish trailing leadcore etc. but it's just the idiots who don't know how to use it. You shouldn't use it unless you are 100% sure of how to use it safely and properly. It can be made unsafe, in the same way rig tubing can, by the idiots that put a swivel behind the tubing, but IMO, companies should show better how to use the stuff!
The new Solar stuff is good, comes with instructions etc, but I use the ESP leadcore, and it's brilliant stuff!
I feel more fish will be damaged by mainline lifting scales from people that don't use tubing or leadcore, and in my experience, the people harping on about fishcare at the rig end are the ones that are worst when they get the fish on the bank! I once talked to a bloke for half an hour, about the importance of breakaway leads and rig components, only to see him, 5 minutes later, put a 12lb carp on a wooden platform to unhook it, and then throw it back, from the comfort of his chair!
The mainline will break anyway, as it's weaker than the leadcore, but it will still have the same pressure exerted upon it if a fish does go for the snags!
Another thing about lead clips, what happens if you crack off, and a fish takes the bait, hooking itself in the process, it'll end up trailing your hooklink, lead, leader/tubing, and X amount of line!
This is why, 90% of the time, I use running leads, or helicopter rigs with a weak link of 3lb nylon tied to the lead.
However, if I do use lead clips, I use the ESP ones, which I've had 4-5lb carp on, and when they shake their head, it discharges the lead! Which, I think is great, because, as I said before, if you crack off, it'll leave an effective rig on the lakebed, whereas with the ESP clips, the fish can just shake their head to lose the lead
I'd rather lose a 50p lead than kill a fish, any day of the week.