I have an Axiom Journey rack, which is also rated for 50kg. No way I'd put anywhere near 50kg of stuff on that rack, it got a bit wobbly with about 13kg. I'm sure structurally it could probably hold 50kg without breaking anything, but I'd never attempt it. Not sure if that was due to the thru-bolt non-threaded eyelets I have on the rear or the fact I bought an adjustable rack, but while it worked, I wasn't the most impressed.
Those original SKS fenders you posted are also what I have. Flimsy but cheap, they work, and work well. Not sure how durable they'll be years down the road, but for my purposes (almost the same as yours) they were a great budget add-on that kept me dry in rain.
Bags? Dunno if they ship to the UK (or are cost effective if they do), but I bought a set of waterproof bags from Nashbar for about $50 with sale and a super coupon day. Not a fan of the attachment system, but I doubt a 14GBP option will be any better, and the the things are utterly waterproof and hold a lot. Or, you could do as my uncle told me, and just line non-waterproof pannier bags with plastic garbage bags
Last edited by jefnvk; 06-06-16 at 09:19 AM.