Tom, I have this lens, got it as part of my DSLR starter kit a couple of years ago.
How shall i say this? It's £99 for a reason. It needs to be stopped down to at least f8 to get anything like decent sharpness. It has no stabilisation, so you need fast shutter speeds with the narrow apertures, so it's only good in very bright conditions. The AF is quite tardy. It suffers badly from CA in contrasty areas. AND more importantly, at the focal length you probably want to use it (like me), 300mm, the image it produces is very very soft. The macro is only 1:2 and is limited to between 180 and 300mm of the range, unfortunately this is where it's sharpness drops off as well.
I'm not doing a very good job of selling my lens, am I? (Seriously you can probably get it even cheaper off ebay).
Please read
this review which is quite accurate in my experience.
I can't remember whether you're a canon man or not, but to my mind you're better off saving up a few pennies and going for something like the 55-250 with IS, which is only around £200 or so. Buy an extension tube and you've got a closer focussing facility as well.
Hope this helps.
Cheers, Sie