Here is my attempt at creating a very difficult Killer Sudoku.

I would be interested to know what others think of it, it is not always easy to judge the difficulty level of my own puzzles. It can be done without using trial and error or guessing.

Thanks for this puzzle.
I've found it not so hard as I expected (according to Patrick's web: 5 stars, subjectively 4.8–4.9 or rather 4 than 6 stars ), but there are some interesting/original points that I registred, e.g. the smallest ‘14’ cage as an unlocker, some naked doubles and triples, importance of the big cage, finding the right combination in the top right corner; and one 2 × 3 unique rectangle, which can speed up the process (but here not so much).

Thanks kozibrada for your interest, looks like I have to try harder . I had not considered the top right corner too much, I had adjusted that area a couple of times because it was helping too much, but looks like I missed something. I will have to try again.

If you want, send it to me in the "user puzzle" format, I'll let you know what my Killer Sudoku solver thinks of it

Ok, I will do that. I am already working on a new puzzle.