Tonie Boxes and Yotos are basically identical in function..
Tonies you out figurines op top.
Yoto uses credit card style RFID cards.
Yoto has a mini version for out and about,
Yoto arguably has more longevity as kids might outgrow the figurines, but cards not so much.
Also, storing cards is much easier than figurines.
Tonies is easier to control by the kids when younger, but at six this isn't an issue I shouldn't think.
Tonies figurines are more expensive than Yoto around £15, maybe more.
I know you can also use the yoto app on your phone to play the cards, uploaded content, podcasts etc you can also control the Yoto from your phone. Including things like remotely setting the volume etc.
(I don't know if Tonies does this, it may well do)
We live our Yoto, but they're both great choices!