Specialized: for 12" sock needles and a belt around the waist as defined by jeans. It works for an over stuffed chair, or knitting in the car as my wife drives. With 6 needles, it works for sweaters, but has the spring action and speed of long gansey needles. It does not fall out and get lost, when out and about. Is it different? Only by fractions of a millimeter, and that makes it better for some specialized purposes.
Given modern a costume of jeans, I would say it has taken me a long time to spiral toward an optimum knitting sheath design. It attaches to a belt as used in modern pant design, it allows use of long (12") needles, and it does not get lost when one is out and about.
Mostly, knitting sheaths allow me to knit objects from fabrics that I would not consider with hand held/ circular needles. Note that I did not say that circular needles are bad, only that I do not consider them as practical tools for some objects knit from some fabrics.
The sock fabric above is good for hiking socks. It is a 6-strand cabled, 840 ypp yarn knit on 2 mm needles at 7.6 spi and 10 rpi for 76 stitches per square inch. That fabric can be knit on circular needles, but the progress will be slow and arduous. I like fast and easy knitting.
Note that this knitting sheath also fits the 1.6 mm needles that I use for other sport socks knit at 11 spi and 13 rpi for 142 stitches per square inch from 6-strand cabled 1640 ypp sock yarn.
And, I use the 12" - 2 mm needles for sweaters these days, so it is has become my work-a-day knitting sheath, and it is not really that specialized - it is worth getting right.