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Hi Roger,
These eyepieces are all much easier to use than plossls - eye relief is generous and the same across the entire line, and all with a nice big eye lens.
I often use these TMBs with my lunar sketching. I typically spend two hours on a sketch, so the eyepieces need to be comfortable to use with the hundreds of times I go to and fro from EP to sketch pad. Plossl eyepieces are just not up to the job.
I have a few of these in my kit that I am keeping. These particular eyepieces are duplicates on focal lengths I already have covered.
Exit pupil is given by dividing the eyepiece focal length by the scope's focal ratio. Exit pupil is one aspect you can use to determine the suitability of an EP. Another is the max magnification a given aperture can do. For your SCT's, the 4.5mm is right on the absolute shortest focal length EP. The 8mm will give you 250X on your C8, which is often the max I can do in my 8" SCT. The 4.5mm you'll more often use with the ED80.
The pic below shows a 9mm TMB Type II next to a 9mm plossl. The other focal lengths of these Type II's pretty much look the same as this 9mm.
I hope this helps.
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