Funny, I had to recently send my Tamron 24-70 in for focusing repairs.
Regarding the 150-600, as with any lens, used in the hands of an experienced photographer, an average lens can take great photos. I really never had any complaints (other than low light shooting) before selling my Tamron 150-600mm as it is an excellent super telephoto for just under $1K. The next step up for a faster 500/600mm lens is several times more expensive.
