As an educator who has personally used Plickers in the classroom and had informal conversations with colleagues who also use it, I would recommend Plickers with one condition: you, as an educator, must be willing to invest your time and effort into using this tool effectively.
To elaborate, the free version of Plickers restricts educators from creating sets with more than five questions. Although there are workarounds, such as creating multiple sets for one lesson, the time required to do so may not always be worthwhile for educators. In contrast, when I need my students to review a lesson or unit in preparation for a summative assessment, I heavily rely on Quizizz or Edpuzzle. These platforms offer a wide range of pre-made assessment materials while also allowing me to create my own.
Formative assessment is most effective when it is timely and provides instant feedback. Unfortunately, Plickers falls short in this aspect due to the upfront workload required. Although Plickers has an "Explore" section, it currently offers limited content, focusing primarily on Early Math, ELA, and high school Biology. This is not yet comparable to the extensive coverage provided by some of its competitors. Additionally, if you stick to the free account, you are again limited to just five questions per set.
Plickers is in the process of developing more curated sets across various subject areas. However, until those become readily available, I would not recommend investing in or paying for the subscription account of Plickers.