[robski]

As with most budget lens they have a sweet spot and if your work within that sweet spot your get some decent results.

So in good light where you can stop down the lens to f8 - f11 and keep to the 90 - 200mm of the zoom range will be it's sweet spot.

Workable for static subjects.

Wide open at 300mm will disapoint with soft images.

Another lens to consider is
70-300mm F4-5.6 APO Macro DG which maybe a tad better.

So what will paying more give you.

Normally a better build quality which is useful if this is your everyday lens.

Faster AF motor good for subjects on the move.

Improved optics that tend to be sharp wide open and less prone to colour fringing especially on the border of the frame. Even sharpness across the frame.

The 90-300mm is good for the money as long as you know it's limitations.

If you are serious about bird photography it won't be long before you meet these limits and you have to dig alot deeper into your pocket for some quality glassware. Secondhand quality glass is still expensive in terms of the 90-300mm.