This is the same deal as in March - 50% off of Pro($25) and EX($109) new keys and also discounted Upgrade($84) from Pro to EX for existing Pro users. Sale ends 1am pst June 22nd(6/22/21).
Previous years they've offered this same deal in March, June, September and November. 2021 is shaping up the same: March and June have happened, so it's likely to go on sale again in September & November. Most of the year you could easily grab the free Trial(3 months on Windows & MacOS) and limp into the next sale period if you're in between sales.
They also have the upgrade from Debut(which you'd find bundled with drawing tablets) to Pro for $25 - so no advantage of the Upgrade vs just buying Pro directly.
The keys are One time Purchase - can be used to activate Windows, or MacOS version of the store. Doesn't work for the iPad(requires subscription), or Android versions.
Key is emailed to you after purchase, key activates in program.
Going way back this program was originally sold in the US under the Manga Studio branding(if you've got an old Manga Studio key, it still works with Clip Studio).
Reasonably comparable free alternative is Krita(https://krita.org/)
March deal thread: