No personal experience of the Kiprun but it looks good on paper, and based on experience of other Decathlon own-brand stuff, I reckon it would be well worth a punt at that price.
On the screen size, the question really is how big do you actually need it to be? It looks like it is about the same screen area as my Forerunner 620 and I find that perfectly useable while running, with 3-4 data fields displayed.
Claimed 7hrs battery life, which is good for a running watch. Even if real life numbers are less than that, it's likely to be more than sufficient unless you're a serious ultrarunner. I get up to around 6hrs from my FR620.
PS this thread might be better moved to the GPS section if you want relevant responses.