There are generally good.
It's all either pattern or original supplier stuff.
I've had one or two dodgy items from them.
A React back box that choked up the Panda and a wishbone on my Jag that's thrown the caster and camber out (and there no adjustment), though I don't think you'll have a problem with the leads.
Given the choice of the same parts, try steer towards the German stuff, Lemforder, Bosch etc.
http://www.gsfcarparts.com/
(another supplier) have moved away from only doing the Frog, Kraut and Turnip stuff and are now doing most car stuff.
Euro has a sister site, it's mail order rather than pick up and is usually a little cheaper,
http://www.carparts4less.co.uk/
Both Euro and GSF have discount codes floating around the net.
Usually forums like the Corsa one throw up the code with the biggest discount.
I've a 25% Euro one, but you need to spend £20 min (though it's disabled when they have a sale one, like now!)
Other good suppliers of different parts.
Tyres -
http://www.camskill.co.uk/
Plugs, O2's etc -
http://www.sparkplugs.co.uk/
Brakes -
https://www.brakes4u.co.uk/
and good old Ebay!