I've carried a Spyderco Ladybug for over a decade. If you get the serrated blade (and you should), you'll want a sharpener that works on them. The closed length is about 2-1/4" (57mm)

Note that it has a locking blade, which makes it illegal in the UK, even though the length is under the limit.

https://www.gov.uk/buying-carrying-knives