I have a Tamron 500 f8 with a Nikon and a Leicaflex adapter and have had it for years. Like others said it is not the sharpest knife in the drawer but it is a 500mm. The rotating tripod colar and rear filter set came with it plus a decent storage box.
The lens does give acceptable results for what it is. I rarely sell off lenses so I still have it. I get it out about once a year in the spring. I've been baiting tree branches with fruit and seeds trying to get a nice set of bird images. It is good for that kind of work because I can prefocus and wait. Biggest problem there is I hate to wait.