Tamron, back in the '80's and 90's so dominated the indie telezoom market, with their Adaptall 80-210mm f3.8-4, which at a good price, almost uniquely, actually delivered a quality that was usable at any setting, including wide open at the long end. It sold in its 100,000's, if not more.
Times have moved on and zoom ranges extended, as are us photographer's expectations. 70-300mm is now the basic norm, with some sort of close focus a feature many hobbyists look out for, as an added bonus.
As a semi pro, using the full-frame Nikon D700, I only had reason to try one of these dinky lightweight lenses whilst waiting for an insurance claim on a broken, much more pricey Nikon equivalent. The cost then, on special offer, was little more than the Excess that insurance claim incurred! I now use as my telezoom standard Tamron's flagship model, their Vibration Control, Ultrasonic Motor A/F Superior Performance, at nearly three times the price.
Yes, there are differences, but not so big as perhaps one would imagine and shots I'd taken with the cheaper lens at London Zoo, for example are not wanting in any department. It uses (so I am informed) high grade plastics for some of the elements - glass is heavy - and why not? My spectacle lenses are plastic! This keeps the weight down and probably the cost too.
Up to about 200mm, it is bitingly sharp, with high contrast and pincushion distortion (straight lines at frame edges bowing inwards) fairly well controlled. My much heavier Tamron is market-leading in this respect but for most, and for most subjects, the cheaper lens won't disappoint.
At 300mm, yes, the images are fairly soft but good contrast still produces pleasing images. If you want to enlarge to A3, from a shot taken at 300mm, you might be disappointed, whereas A4 should be fine. I haven't used a 'cheap' Nikon lens of this spec, though even expensive ones aren't so brilliant either and my flagship Tamron beats them in any case - in my experience).
I do recall the macro 'feature' as being useful (though I own a specialist macro - another Tamron!, the 90mm f2.8) so I didn't rely on this but I did try it out. Image quality was actually very good, especially for flowers and natural things. Yes, the switching to - and from - was a bit fiddly and made it impossible to track, say a butterfly, if it flew out of the macro's zone of focus.
But, on the basis of value/features/spec/quality, in roughly that order, then how can I not award four stars? It got me out of a jam and I keep on finding images that I'd taken with it and for the large part are they are indecipherable from the others, unless one really zooms right in and examines 'actual pixels' on a big computer screen.
For those on a budget, or those whose first telezoom this is and don't want to make an expensive mistake then this dinky Tamron comes quite highly recommended; by someone who still has one of those old 80-210mm Tamrons from thirty years ago! (- which I no longer use, I have to add.....)