The lens will be good for comet imaging, as it is fast enough to allow short exposures to stop the comet trailing against the stars if unable to guide on the comet itself.
With the lens, Im plesantly surprised how east its all worked. The supplied mounting rings have holes in the bottom that allow it to be easily and firmly bolted to the base plate of my mount, as shown in my pic
http://www.users.on.net/~josiah/mod350d/300mmlens.jpg
In nearly all directions, when I attach my illuminated reticle eyepiece holder I can sit in a garden chair while I guide, nice and comfortable, and my 2 inch filters fit nicely into the camera adaptor part of the lens. Its a joy to use.
Scott