They are incredibly addictive and absolutely adorable. Each cup begins with a provisional cast on and is knitted flat, back and forth. Each one consists of four short segments and you've got the anticipation of a turn to look forward to, as well as seeing it take shape.
I've made a number of them over the summer and thought that it looks particularly fetching in variegated yarn; you can see the bursts of colour change and highlight the bias shape of a cup beautifully.
The cups are all 3 inches / 7.5 cm in diametre, perfect for a similarly sized cup (or a bottle) with varied lengths; two were knitted in a DK weight and one in a very light Worsted weight yarns. Ideally you'd like for your garter stitch to be quite firm here to hold its shape a little and I would advise erring or a slightly smaller needles than you'd usually use for a DK gauge.
The size can be easily adjusted by altering the number of garter ridges you work in between pivoting points.