It was dog slow and it had some really stupid api you had to use if you needed to handle nesting that you couldn’t determine until runtime (on account of the no closing tags—use case: rendering a tree of data in a streaming-records sort of situation, not exactly a super-rare need).

There was a faster implementation, several times faster… but it achieved that in no small part by ditching the bits of the api that allowed you to manipulate nesting, so I couldn’t use it.

That project made me hate crap like this. HTML isn’t scary, hard, or even (in a halfway modern editor) slow to write, FFS. I’ll never ever pick this sort of templating language when it’s my choice.

As for adding a layer to what devs needs to learn - that's why I don't generally use this at work. In those situations you often need to pick the most common tools and not the best tools.