This is a 28-388mm equivalent lens, adding 50mm to the tele end and does so at no cost of weight, dimension, or optical performance over the older Tamron’s 18-200mm f/3.5-6.3 lens. Only the price is higher: at $499 (street), vs. $390 for the shorter lens. Here’s a quick summary:
“Compact and light, it’s about the same size as the 18-200mm. Attractively finished in a satiny matte black, with ribbed and rubberized zoom and focusing rings (the former large, the latter on the small side), the lens sports the bright gold Di II band that distinguishes all Tamron digital-only lenses.

We found its zoom action slightly uneven, somewhat stiff and overdamped, which rendered the zoom lock unnecessary. AF action was fast and quiet. On the Canon EOS Digital Rebel XTi, with the lens barrel fully extended, it cast no shadow when used with built-in flash.”

Website :  Lens Test: Tamron 18-250mm f/3.5-6.3 Di II Macro