I saw this in a charity shop for £10, it looked in good condition, no zoom creep. Not the sharpest of lenses and a minimum focussing distance of 2 metres so not a great lens.
Robert it doesn't matter if the lens is pin sharp, I consider the fact you got it cheap and was able to use it on a more modern camera. This is what photography is all about, being able to learn about a lens and use it. Photography is a adventure and this is what makes it fun.
At this web size it looks sharp enough to me. I've seen plenty of images less sharp than that one. It's worth keeping and using occasionally,
I am not too worried about the lens as I have a Tamron SP 60-300mm that is actually a lot sharper (in my opinion anyway) but the Sigma does have an A-M switch so I can use it on my Canon, unlike the Tammy.