Thing is, there isn't any other lens out that is going to give you decent IQ at 1350mm. You could spend over 12K for the new 600mm and put a 2x on it and the IQ would be marginal. To me a bad picture compared to a picture that is just a little bit worse is about equal. I think it would be worth the value if the IQ doesn't matter, which it wouldn't to me at 1350mm because nothings acceptable at that length.

At 650mm I wonder if you couldn't find an old super telephoto lens and adapt it somehow and be better off. I see a few pop up every once in a while on craigslist that are very cheap.

But there would be one good use for this lens, if you already own one of the long supertele's and one of your buddies asks you to lend him one of your long lenses. If you owned this one it would be the good loaner.