Students can learn a lot from each other. The students then get back into their own groups and discuss what each learned, and how the project will proceed. The groups present their work to this point to the rest of the class. This format generally takes the most class time, but it helps the students practice for oral presentations to large groups. Three or four times during a project is not too often to have design reviews.
Students get better at critiquing the more opportunities they have to learn that skill.
Each review, as a rule of thumb, should be about 10 minutes long. Demonstrating the kind of comments you want the students to make is crucial. This helps limit unconstructive criticism. Have the students focus their comments on the evaluation criteria that you and the class have generated. This also limits unconstructive comments.