The medium sized calipers are the most popular- they are used by artists, graphic-designers, engineers, plastic-surgeons and gadget-collectors.
I personally use these ones for web-design – to get a “2nd opinion” etc… and am increasingly using them for painting.
They come with a laser-cut, magnet-equipped case. The dark hardboard ones come as standard, but other options are available as well.
For an extra $10 I can put your logo on the case – if you send me a file, I’ll send back a mockup image.