It's good quality equipment. I've used their fuseholders (which, contrary to Nigel Calder's dire warning, don't melt and don't come loose!). You can find Blue Sea products in better chandleries. I know Fox's Chandlery in Ipswich stocks a range of Blue Sea stuff, and they'll happily do mail order.
The Blue Seas gear is good quality, if a little pricey. The two main dealers are On Board Power in the Hamble (023 8045 8600 www.onboardpower.com) and Merlin Equipment in Poole (01202 697979 www.the-power-store.com). Also, many good chandlers stock it.