I was the instigator of this thread originally. I bought a used Tamron 18-250 and its been fine. I believe it is slightly higher rated than the 18-270 on Dyxum.
My walk around lens is the Tamron 18-50 2.8 and it is a very good lens. I now want to buy a good prime lens plus after visiting Cades Cove in the Smokies, I really want something with more reach. I would love the Sony 7-400 G lens but its out of my price range. I am pondering the Tamron 200-500.
Before you buy, give KEH.com a look along with B&H's used lenses. My 18-250 looked brand new and I think I paid about $250 for it.