We used to have a TonieBox but I found them incredibly restrictive. Also I thought that the physical design was poor. Because the figures just sit on top of the box, you cant move it around whilst playing it or the figures just fall off and the audio stops. It was very frustrating watching my kid try to use it in the car on a long journery. Scrapped that and invested in Yoto player, its pretty much the same thing but…
We were aware of Tonie before Yoto because our children's friends had them and we decided to go Yoto instead, they're amazingly simple, the app is great with well thought out features, and we've even convinced some of those families with Tonies to switch to Yoto and they've also been very happy.
There's a pretty good market for second hand Yoto cards too in the UK though don't expect much in the way of deals, many of them sell for RRP or higher, though we have found some cards our 5yo really wanted but are only available in the US by buying them second hand.
When my 5yo was about 3 we gave her a CD player and bought lots of CDs, funnily she grew to think that was the height of cutting edge technology and digital (virtual) audio was the old tech. Needless to say, the CDs didn't last in the hands of a 3yo, then followed by a little sibling, they ended up scratched to pieces and wouldn't play any more, the card based approach of Yoto is much more suitable for young children, and the kids are learning lots, they particularly love the audio adventures.
As much as I'd love to hack the thing, I feel the same way another commentor does, that it shouldn't be touched, though I did manage to grab the URL from my OPNSense for the night time radio so I can stream it in my office because it's pretty good.
I am a little cautious that the cards only contain a URL and we don't actually have copies of any of the audio for the cards we've bought (other than what's in the device's cache); we have somewhere in the region of 200+ cards now; which is quite an investment, and it's very much at the mercy of Yoto and their servers remaining active and accessible.