The manufacturer does recommend backwashing by blowing water out of it at least daily (it was designed primarily to be used daily, after all). However, the flow rate from one of their online docs does show a flow reduction over time, which is certainly not unexpected for a sealed product like this. The backwashing probably mostly clears sediment from the more coarse pre-filter portion on the tip. Not sure if it does much for the interior parts.

I read another doc where a lab did test up to 1,600L (so 160% of rated capacity) through the Lifestraw and I believe the purifying performance was still satisfactory at that point IIRC.