Unknown aspects to BIOS update - MEFW and Signed Firmware Update - what are they?

MEFW stands for Management Engine FirmWare and it controls how the onboard Intel management chip operates:
en.wikipedia.org/.../Intel_Active_Management_Technology

Signed Firmware Update Feature would refer to the system's ability to accept updates from signed update files/sources only, helping prevent some types of attacks designed to roll back to a previous version with a known security flaw.

Also, keep in mind that BIOS updates are "cumulative" updates, meaning that A20 contains all the Fixes/Enhancements in all the previous updates as well.  What is your current BIOS version?

You can do without these if you don't feel comfortable doing the update (although the "improved" ME firmware may improve the problems you have with AMT, although I've never had an issue with AMT).  You have everything but this latest update, so you should be fine.  AMT doesn't add any price difference to the system - you just sacrifice other features that you could better utilize, rather than features you can't use.  Just remember to shop Home systems for home use and Business/Office systems for business/office use.  The only good reason for them recommending a business line of PC would be if you stated a need for increased stability and compatibility with business software (including OS) or hardware, regardless of where it was to be used ... cutting-edge consumer hardware is not the place for that.