Boox had a new product launch event thingy last night and several new devices were officially announced, including the Picco, so while most are not available yet, there are official product pages on their website with specs, including the price.
Looks like the approximate price for Picco is going to be $100, so directly comparable to the Xteink X4 Pro. No idea yet about the release date.
https://shop.boox.com/products/picco
It looks like it’s using pretty much the same ESP32 system and same lower PPI (235 PPI in this case) screen as the other small pocket size competitors.