Yes, my eldest went in y10 and had a great time. She's now in y13 and the one hoping she's made the Kangaroo again this year - she's not doing FM A level as her passions lie elsewhere
She was saying that at GCSE level they had loads of time to do UKMT questions and other interesting stuff but now it's all just work work work.
My y12 dd claims not to like maths, but is doing it as an 'easier' A level option as she did 2 modules in y11. The kids were checking their answers when they came out the next day, and adding up their scores, and she might have got a silver. The other two were consoling her with the assurance that that means top 30%, lol.
And my son answered more questions than his big sisters and thinks he got them all right. He's not sure he actually knows enough maths yet to do justice to BMO1 if he happened to make it over that threshold, depends on this year's boundaries, although I reassured him a bit by showing him this histogram
which shows the most common mark as being 3!