I compared outbound business class and return Joyful Economy in April 2024. For me, the business seat and leg support were more comfortable than simply having an empty middle seat.
First-hand experience from 2024. Menus, prices, opening arrangements and service conditions may have changed.

Outbound business class
I paid KRW 130,000 per person at Incheon Airport to change to business. The seat was not fully flat, but had a reclining backrest, leg support and more space in front. There was an overhead shared monitor rather than an individual screen. The meal was ordinary; I enjoyed the fruit.
Return Joyful Economy
We paid KRW 135,000 per person. Two people shared a standard row of three economy seats, with the middle seat fixed as a table. The seat itself was not larger and the row could not be used as three unrestricted seats. We received blankets and slippers, and the extra side space was useful for bags.
My preference
At a similar additional price, I would favor business. All amounts and features are those offered on our particular 2024 flights; confirm current availability and terms.
Trip-planning reference
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