Sly Flourish's "Luck Replacing Inspiration" in D&D is +3 to players

We used Sly Flourish's Replacing 5E Luck With Inspiration in our last 2 sessions and everyone loved it after a few reminders to "you miss, but turn your luck die" (everyone has a D6 in front of them with 6 indicating 0 luck).

But this mechanic, unlike inspiration, happens a lot. So I wrote a quick computer program to calculate how often luck could be used to make a roll. The answer is a little over 15% of the time, which is the equivalent of +3. So, as a DM you probably want to add +3AC to all your monsters and relevant DCs to maintain the same difficulty: there will be more initial misses, but the players will be able to use this mechanic to balance things out again.

Since the DM can award luck just as they can award inspiration, you aren't nerfing the mechanic by upping the AC/DC: the players just have a new mechanism that (in my short experience) helps with the save-or-suck moments.