Should I buy a grinder?

Sup,

Never actually owned a grinder before. Found this sweet masterdam grinder on amazon.

Question is, do I get it? People have told me they don't grind for bongs, and I normally use a knife and cut it up. Is the grinder worth it? Can I just use it enough so it's not fully ground + will I be able to collect some good kief to smoke later?

I'd get the 40mm one. Cheaper lol

Cheers