The biggest weakness of Pear Deck is that student work often comes out messy. This is not the students' fault, it is hard to write on the screen, especially if you don't have a touchscreen. This is an issue because slides are too small to show adequate work. This problem could be solved if somehow a scrolling feature could be added to the slides where students are asked to "draw" so students could have more space.
Students do have the option of putting in text boxes, which helps with the neatness and sloppiness, but there isn't a feature for students to put in equations or special characters. This is an issue in math classes because students cannot show exponents, Greek letters, etc.
While Pear Deck does allow teachers to provide better feedback, there is no way to actually put in feedback ON the slides (i.e. leave a comment on a student's response or better yet, write on their work). Students are also unable to see each others' responses, although you could link to a website like Parlay, Nearpod, or Padlet for students to contribute to a discussion.
Pear Deck does come with a 90-day trial, but unfortunately, it isn't free.