I was looking at immersion heaters this evening in B&Q the plumbing section, which to be fair was very good. It is very advanced nowadays. But anyway, I saw INCALOY Immersion Heaters which were an extra 10pounds on top of normal immersion heaters. 27ounds instead of 17! What exactly are these and are they worth the exgtra money? Are they longer ladting??!!!! Thanks all for your help!!