I’ve seen people object to a 13 month calendar based solely on the idea that you can’t divide the year into quarters. But it’s actually really easy to remember. A quarter is 13 weeks, or 3 months and 1 week. So Q1 ends a week after month three, Q2 ends 2 weeks after month six, Q3 ends 3 weeks after month nine, and q4 ends after month 13 aka the end of the year. And since the calendar doesn’t change, you don’t even need to remember it, just mark the quarter ends once and you’re done forever.

Just compare that to the unnecessary complexity of the Gregorian calendar and the effort it takes to remember basically anything that changes from year to year, or what day of the week any given date or holiday falls on, or even just which months have 30 days and which have 31.