I have got this lens with a Pentax fix and I am incredibly happy with its performance! I think it has a really impressive range so that you can do some really nice close up shots but also get some nice wide angle shots. Additionally, tamron lenses are made from glass, and although they are a little heavier, I think that you can really notice the difference between the glass and plastic lenses.
They are quite pricey, however If you have a good camera body then it is definitely worth spending a little more on a professional lens.
I also think that they have a nice grip around the lens which makes it really easy to zoom in or out. Additionally please remember to buy a UV filter protector which fits at the top of the lens to keep it protected. Another useful point to mention is that when you twist the lens, it does compact a lot so it fits in most of the cases.