Bought the kids headphones for Christmas, Airpod Max for the eldest and some XM4's for the youngest, both on the Very BNPL 20% off deal (so £387 for the Max's and £170 for the XM4's).
Youngest had another few pressies, whilst the eldest who is into Apple products (like a lot of the kids these days, was happy for the bulk of her present allowance to go on the Max's).
I've compared both side by side, and I'm definitely more impressed with the Max's, I tend to like a brighter sound that is less bass heavy (I do like bass, but not at the expense of overall clarity). I can only describe the sound as being 'wider' than the XM4's (the XM4s are still excellent as well though, and a bargain for what I paid). There is still plenty of bass on the Max's though, less than the XM4's, but I'd say more precise sounding.
I'm gonna add these to the Apple Care as well, eldest very careful with her gadgets, and they'll probably never leave the house (she has airpods for that, and I'd be scared of some scrote stealing them on the basis they are so visible), but I have read of the issues with condensation.......but I'd gather that's probably more an issue if you are taking them on the move with temperature changes, and maybe weather exposure.