Is the CMYK accurate for printing?

It is the standard conversion, which is what any screen based tool can honestly give you.

What is HSL useful for?

Adjusting a colour rather than describing it.

Convert a colour

Pick a colour and read it as hex, RGB, HSL and CMYK at once.

Hex

#b4530a

RGB

rgb(180, 83, 10)

CSS rgb

rgb(180 83 10)

HSL

hsl(26, 89%, 37%)

CMYK

0%, 54%, 94%, 29%

CMYK here is the straightforward conversion, which is what any screen tool can honestly give you. Matching a specific press needs that printer’s own colour profile.

Questions

Can I paste a colour in rather than pick one?: Yes.
Is the CMYK accurate for printing?: It is the standard conversion, which is what any screen based tool can honestly give you.
What is HSL useful for?: Adjusting a colour rather than describing it.