I did use one once. It was nice. Real clear night. We used it with a 40MM (1.25) eyepiece to get f/6.3 instead of f/10. Brought the magnification down from 76x to about 50x. M101 was spectacular. It was smattered all over the field. Pieces of it were everywhere. All the brighter areas in photos were visible. Sprial structure was very apparent. Couldn't see as much of it at once with the 40MM alone at 76x. I didn't have any of my good eyepieces yet. This was when I first got the scope. Now a focal reducer will increase the actual field (amount of sky your looking at) by reducing the magnification. But it dosen't increase the apparent field. Even though we were looking at more sky, the apparent field size was still the same. The apparent field is how big the circle your looking at is. It's like the difference between looking at a 19" TV and a 35" TV, it's the same picture only bigger. So a 40MM with 67 degree field will show the same actual field as a 40MM with 52 degree field, but the circle or image will look bigger. The same 2 eyepieces with the f/6.3 focal reducer will have no effect on the apparent field, just the actual field. So you do still need the Nagler 31mm 82 degree eyepiece. Or at least a 67 degree size. You'll see the difference.
That's it;
BOB SAL