Is this set still useful for modern Technic builds?

Yes, as a collection of 100 connector pegs, this 2014 Technic piece can be used for repairs or specific Technic projects.

What is the theme of this specific peg set?

The theme for set number 5003121-1 is Technic.

This set includes a total of 100 pieces.

Name: LEGO Connector Pegs (5003121-1)
Brand: LEGO

Technic

Technic · 2014

Theme · TechnicPieces · 100Set Number · 5003121-1Year · 2014

Used

—

New / Sealed

—

Live on eBay now

Converted from USD at the ECB reference rate — sold comps are US-market sales.

JunkPal AI· resale insightanalyzing sold comps…

▍

Is this set still useful for modern Technic builds?: Yes, as a collection of 100 connector pegs, this 2014 Technic piece can be used for repairs or specific Technic projects.
What is the theme of this specific peg set?: The theme for set number 5003121-1 is Technic.
How many pieces are included in the 5003121-1 set?: This set includes a total of 100 pieces.