Just brought a new air flow meter off ebay, was £32 and works fine, but think my fuel economy has gone down.

I am getting at best 300 miles for a tank £40 at £1.24/litre. Does this sound OK to you or should I have spent loads more money on genuine Nissan part? It's an X-reg Micra with 40.000 miles.

I have looked but can't find anywhere that says what the fuel tank range should be. Slow driver: A1 at 60 mph. I drive for best economy.