The original Miyoo Mini is about the size of a deck of playing cards. The manufacturer followed up this device with the larger (but still pocketable) Miyoo Mini Plus, largely due to the lack of availability for the smaller screens.
There are various "versions" of the original Miyoo Mini: version 1 has a pop-out cell phone style battery, while the v2 has a slightly larger-capacity battery with a wired attachment (and a few other slight manufacturing differences). The "v3" and "v4" devices identify later production runs, though it's not clear that there are appreciable hardware differences – though the v4 does use a different screen, which needs the latest version of the Onion OS firmware (v.4.3 or later) to fix some resolution and color issues.