The plugin (the free version, that is, without the non-free manual) provides an amazing number of options, like shortcodes and templates, for customization. Unfortunately the customizations readily available are somewhat limited. I came away feeling like I was given a jetski to ride around a wading pool.
For example, what are the PHP tags? Another example: Why are day, week, and month the only time intervals for which events can be displayed through the
[my_calendar] shortcode? What if one would like to show events for a different time range, or even (dare we imagine?) ALL events?
I installed the plugin looking for a quick solution to my client's desire for a simple events calendar. Unfortunately I lack the time to pour through all the options and what documentation exists (for free), so I ended up going with (the free version of) The Events Calendar instead--the options are fewer, but the API documentation is freely available and reasonably clear.
The unclarity and imposing number of limited options may be a couple reasons that the number of downloads for the present plugin is disproportionately large for the number of ratings. All-in-one Events Calendar, for example, has only 31% more downloads, but 260% more ratings. Could it be that people are downloading My Calendar and, after taking a look at it, moving to something simpler?
A more meta-suggestion/thought is about the business model. I'm trying to imagine why (most) people would plunk down money for the manual of a product that they haven't even been able to effectively try without that documentation... especially when there are multiple free alternatives with documentation out in the open.
In sum, this plugin is an heroic project, but sadly unable to make it all the way to where the users live.