It is a good extension and serves it's function as a speed reader. You can also mess around with settings how ever you like and to your likings. However, the fact that you can't highlight what you want to read really puts this addon at a really disadvantegous place.

Instead of reading where you want, it will make you read the whole page. For example, if you want to read a Reddit comment, it will start from the subreddit desc, the top comments, and then the thing you actually want to read.

TL;DR - Serves its purpose, have good customization settings. You can't read a specific part of a page because you can't select what you want to read. It will load the whole page instead.