Spot on. The size is a legitimate concern.
Although I have come around on the size. They sorta look like the size of NES controllers.
Wrong though, the GBA micro is already 15% smaller than an NES controller in width.
NES controllers are like 116-117 MM wide
The GBA micro is 101 MM wide
CHARITABLY using that comparison photo (to allow for inaccuracy due to it just beign a photo and me using photoshop to check this stuff) the joycon are 95 mm wide. I would guess closer to 90 in reality, like 91 or 92.
The distance between the right side of that analog stick and the left side of the leftmost button is TEN MILLIMETERS. That's like the size of a pencil eraser and the metal on its side. It's less than the size of that entire GBA Micro's dpad width (And that much you can verify just by checking the picture yourself).
To say it's NES controller sized is monumentally wrong, this would be like if the NES controller had about 1/4 of its width shaved off, half of the height, and you stuck the analog stick where select is and the 4 buttons where start are.
My non-scientifically accurate quick MSpaint comparison, utilizing an NES:GBA micro pic and a joycon:GBA Micro pic. This one is obviously approximate but it's VERY close.
EDIT: WHoops, forgot I was the last poster sorry fam.