|A humongous 50mm monstrosity|
What I dislike about them is mostly that they are ugly! However I think there are practical drawbacks to them too. The ring feet on large rings fitted to tip sections are often wider than the blanks, which makes them difficult to whip neatly. This doesn't affect performance, of course, but it's a pain and is not aesthetically pleasing.
What the large rings definitely do, however, is add weight. And the place you least want to add weight to a rod, especially a rod intended for long casting as most are with these large rings, is the tip section. I admit that I have yet to go on the field and try casting comparisons, so this could well be hypothesising with no foundation. Even so, there is a noticeable difference in feel between two otherwise identical rods if one has a 30mm butt ring set and the other a 50mm set. The rod with the 50mm set feels decidedly more floppy. Well, the one I'm building right now does.
There may be a way to compromise and get a better feeling rod using a 50mm butt ring. That is if the people who want them can be convinced that they don't also require humongous tip rings to go with them. By stepping down the intermediate rings more abruptly the ones nearer the rod tip would be much lighter, and the feel of the rod restored.
Changing tack, I got my first glimpse of the Fuji 'K' framed rings the other day. Very nice they looked too. I'll be giving them a closer inspection at the Tackle and Guns trade show on Sunday.