Does Ozone recommend 25m lines on even their 6m and 4m catalysts? Has anyone tried putting these on shorter lines?
It does not matter what Ozone recommends - they would not know in this case
If you like shorter lines on these, just do it
If longer lines feel better, just do it
25m is very long for 4 and 6m2 kites, but used by some as "light wind" lines with a 6m2 kite in waves.
Many like the opposite of what you want - namely that shorter lines gives a more direct response, and the kiteloop is better as it will be "close" to the water surface, so you get up higher relative to the kite, in kiteloops
With longer lines, kiteloops are much easier though - as the kite just "loops around up high" and no risk, nor difficulty level, and not looking good, like short lined kite low loops does.
The "snap" when you whip the kite, is much better with shorter lines - so for freestyle you get a kite where you can change pull direction much faster, especially noticeable in the air and when doing aerial transitions
The other way around - short lines gives a very on/off feeling that I dont like myself (talking bout less than 20m now), and you lose the effortless powerdelivery and backup totally
So the change when changing line lengths is extremely noticeable, for all kites indeed.
Some more than others, because as said, if a kite pulls a lot more with apparent wind (higher AR higher cambered kites typically), longer lines has a huge impact when you fly the kite around.
More "sit stable and grunty low AR pull kites" does often not gain much with longer lines
18 to 27meter is the range used by many as I see it (low wind - high wind - waves - jumps etc), but most often between 20 and 25meter is the most used.