I have two Brita filter jugs, one in the fridge for drinking water and one room temperature one for the kettle and veg steamer. The fridge one takes Classic filters and the kettle one, being a little newer, takes these Maxtra ones.
I'm not convinced that the Maxtra cartridges are much good, or at least, that they're any better than the Classic ones.
First of all (and this could be a design peculiarity of the jug so I won't go into it in much detail here), there seems to be a fit issue with the jug (a Marella) whereby even when pushed down to the 'click', there is a gap between the bottom of the filter and the part of the jug it sits against. An amount of water sits in this gap as the hole through which the water is supposed to pour is slightly raised.
Secondly, the cartridges seem to have to be 'rinsed through' several more times than the Classic ones, as they seem to leak grey water (even after the ceremonial dunking, shaking and double-filtering that Brita recommend on the side of the pack) when new. I understand that this is charcoal and isn't dangerous, but it's slightly gritty and certainly doesn't look very nice.
Finally, in terms of limescale prevention, I'm not sure that the filters are terribly effective. My kettle gets fuzzed up with limescale almost as quickly as if I just used tap water. Having said that, Maxtra filtered water seems to be scum-free for hot drinks, stocks, soup etc so I suppose it must be doing something.
So although it seems to work to a standard, there seem to me to be a few small issues which stop it being an exceptional product. Having said that, now that Brita don't make Classic filter jugs any more, I'm going to have to persevere with Maxtra with one of their newer jugs - hopefully it will fit the filter better.
Also, the price here on Amazon, with the discount, is very good - supermarkets and chemists don't reduce these at all!