I have a 305 and a 405. i've not had any issues with leaking, although the valve on my 405 does leak just a bit while I'm in the process of turning it on or off ( i guess its an o-ring or something)... IMO
, they're great filters, and you made a good choice. Not to say its the best filter on the market, but I would not hesitate to buy another after using a few others. If you keep it cleaned every other week, more if necessary, you shouldnt have any problems with it. I would suggest ordering an extra impeller cover or two, as I've broken two since I've had mine. Keep your intake as high as you can to keep the sand out of it and you should be fine. As stated previously, the water goes through the sponges and media before it hits the impeller, so any sand that does make it in to the filter will get caught in the filter before it hits the impeller.