I rented it locally from lensprotogo.com for the weekend to try it out and to allow my daughter to use the 70-200 on a rented 7D. No complaints with the 300 beyond the excess number of keepers it generated paired the Mark IV. I miss the days of deleting half my 7D shots in 1st pass of post processing as clearly out of focus (not that it was all that bad, it just tossed in more out of focus shots during bursts).

It was a bit inconvenient not to be able to pull back to 70mm for certain, shots but the extra reach was nice and the shots were excellent. One cost barrier to getting it beyond its own cost is the additional cost of a good 2nd body (read 5D Mark III) to work with vs. swapping lenses constantly.