- It took forever to be released
- It's plain looking
- It doesn't have any options
- It only has 1 sidebar
- It only has 1 layout
- It only has 1 menu
That's one way of looking at it, another way might be
- You can do so much with this theme since it lacks any fancy styles
- It's great as is or as a base to create your own theme
- You can learn a lot by adding sidebars, menus and widget areas yourself
- The thousands of WordPress tutorials on the internet explaining how to edit themes will finally be useful to you
- It's well coded
- It works on mobile devices
- It's Free!
You don't have to use rem values in your child theme
You don't have to worry about it not working on mobile unless you don't follow the coding.
The mobile first approach is confusing at first, but it's really just a matter of adding a bit of extra CSS to keep it working on any device.
Plus, it'll give me something to post about on my own site when I make all kinds of child themes with extra widgets, menus, and sidebars for people that don't want to do it themselves. :)