Hey Cathlmg, i use it as well, i swear by it actually. Not that the filter is that small, anyway size isn't all that matters.
My personal logic thinking I suppose. IMHO.
A water filter is for trapping sediments and contenmints between the the pipe before your tap and you. So if it is too small, water flow will slow down because of all these stuck inside. So you need to take it out to wash it often, or have its filters refills changed more frequently. As I have mentioned in my earlier post, strictly for drinking purposes is OK. But if you want to use it for washing, like for example the car or the clothes, the upkeep part is going to be expensive....
Personally, I feel that for washing of cars, the sediments in the unfiltered water will scratch the car paint. Maybe not noticeable on the first few wash. But it will slowly build up to a point where you need to wax the car frequently. Same as for washing the floor, it only makes the floor more sticky and then you have to wash it with more water....