I love them. They are worth it for me because I do live in them during the summer. They are literally all I wear on my feet between May-September and I do wear them until they fall apart. Currently I have plain black Tops for work, black Brasils (a bit worn down), yellow/green Brasils and grey Brasils. I'm trying to work out if I need some metallic ones for this summer or if I could just customise a pair I already have. Agree that they collect dirt, I'd be wary of white/light coloured ones.
However, great tip about the washing machine - I scrub them by hand every few weeks in the summer, but putting them in the machine is genius!
Oh and the difference (in my experience) between havaianas and cheaper flipflops is that havs don't rub, ever, and the weight. Havs are denser, more supportive, comfier, more durable. If you pick up a pair of havs in one hand and a pair of cheaper ones in the other you can really notice it.
OK, I took delivery of my pair from Matalan today and am wearing them round the house. I still don't geddit. They feel like, well, flip flops. I was expecting super comfort. They still feel thin and have sharp plasticky straps and the toe bit.
Still, only paid a tenner for them so they'll do for summer slippers.