This lens was a wish for years.
I got a good price for my 70-300L on a second hand market and the extra aperture (70mm vs 54mm), range (400mm vs 300mm), even better IS and closer focus (0.9 vs 1.2m) is worth it ! And razor sharp images (but that was also with the 70-300) !
Still no real astronomical first light for it (due to extreme short summer nights on this far northern location), but I am very curious.
Well worth the
A$2800 price !
And I tried it even visually: this setup shows the lens + powermate 2.5x + diagonal + Nagler 13mm (77x) and crisp images with this cute little APO scope !
The other setup is a handheld 16x70 monocular with panoptic 24mm.
Here some sample images.
The plane is at full altitude an Iran Air A330 from London to Tehran.