Well, I started to leave a quick reply below, but it turned into a review. I didn't get to leave a rating, so I'm posting it again.
Version 4.5.2 is working perfectly in Yosemite 10.10.3.
While itsycal may have some similar functions, it's in black & white and does not offer the customization or functionality of MCC iCal.
I've used MCC iCal for years and love it!
It does sooooo much more and looks sooooo much better than the Apple clock! Apple's font is monochrome and boring.
There are 19 formats to display the time, plus you can set a custom format. The calendar icon can be displayed in color and I can choose a color for the opened calendar border. I can choose the font, color, and size of the time displayed in the menu bar. It's the only bright spot of color up there! I have it set in a bold font and colored cayenne. It's very easy to read at a quick glance, unlike the OEM font. It can be moved to the left of your other icons if you choose. Double-click a day in the calendar and Apple's Calendar app opens. Would be nice if it could open BusyCal or other calendar apps.
I agree that $20 is too much, especially for what seems to be abandonware, but then it's still functioning normally on the most-recent OS. They could however add functionality to support more calendars. If it wasn't so expensive to begin with, they likely would have sold more copies and might have felt it was worthy of continued support.