Does anyone have experience with the Bobble water bottle?

I’m thinking about buying one of these, but I’m concerned about two things. Firstly, the cost of replacement filters – I know it will be less than buying bottled water, but the main concern is shipping and handling costs from the supplier – how often have you changed the filter?

Second, is the filter actually effective? I know that it’s no good for undrinkable water, but does it improve the taste/clarity of tap water to the point where it’s worth paying for the filters?