I couldn't find specs for this thing but from the picture it looks to be about the same size as the original iPhone.
Touch 4G: 102 x 62 x 11
iPhone: 115 x 61 x 12
The Samsung Z Flip is probably your best bet if small size is the most important factor - though, er, slightly more expensive than the HMD!
Z Flip 7: 86 x 75 x 13
I'm not counting people that did upgrade but are spiteful of the forced size increase.
I'd have got one myself but iOS doesn't work for me.. I have several things I need on a mobile phone that are not available on iOS.
For me a phone is really an outside the house thing only. I don't use it at home to poke around on the internet etc, like most people do these days. I still have a real computer with a massive screen and keyboard. So a mini size is great for me.
On Android there's the ones from Unihertz but they take the "small" factor a little bit too far, and also their software support is absolutely terrible. And people often mention the zenPhone, I'm not sure why because it was never smaller than the Samsung S-series. It wasn't really a small phone anyway.