Let me start by saying this is not a paid advertisement for either whiteboard site. This is a teacher trying to find the best product for her students to help them learn. I suggest you try both and see which one works for you.
We are currently not hybrid [1/2 at home, 1/2 in person each day] but I can’t get everyone to the whiteboard at the same time now that we have everyone back in person. I LOVE to have all of my students working on problems at the same time so I can see misconceptions. My district blocks Jamboard (IDK why!) so I began looking for other options.
My friend Melissa (@fungooli) did a comparison of whiteboard.chat and whiteboard.fi on Twitter so I decided to give whiteboard.chat a try. I had tried whiteboard.fi previously. At the time, not all of the features were free and it was super lagy (is that a word?). I checked it out again for this comparison and some of the features, such as saving your board, is still premium. Below is Mel’s comparison of just the feedback portion of the two.
https://platform.twitter.com/widgets.js😅Not sure if this is useful or not. 🧐I just had a look at the options for #studentfeedback in @WhiteboardFi and @WhiteboardChat .
— mel a (@fungooli) January 9, 2021
I haven't used #whiteboardchat with kids yet. There are a lot more features.🤔
👉https://t.co/YV2AmccU7n#iteachmath #edutwitter @loom
I’m a huge proponent of feedback so the feedback feature in whiteboard.chat was super important to me.
I like the math editor available in whiteboard.fi better, but it’s still lags, A LOT! My student’s computers are not the best and that lag would be frustrating for them. There are some math tools in whiteboard.chat just not in latex format. For what I’m doing, I don’t think that will be an issue.
You can upload a PDF in both. I created a PDF warm-up in Google Slides and used File-Download as PDF. Then uploaded it. It was easy to do in both sites.
The tools for students are more intuitive in whiteboard.fi which means I needed to take some time to explain the tools in whiteboard.chat. Not a deal breaker, just something to note. Tools for teachers are easier in whiteboard.chat. I also like that I can create my board ahead of time because it doesn’t require purchasing an upgrade to save a board.
Overall, I like whiteboard.chat the best. I didn’t actually send whiteboard.fi to my students so I can’t tell you which one they would like the best. Students got the hang of typing their responses using the keyboard. Some were frustrated with writing on their trackpad. Our student laptops have terrible track pads so I feel their frustration. Overall, whiteboard.chat accomplished what I wanted. I still prefer sending my students to the whiteboard when possible 🙂
Here is the first warm-up slide deck I used with my Honors Geometry class. I downloaded it as a PDF and uploaded that into whiteboard.chat.
If you try it out, let me know and give a shout-out to Mel (@fungooli) who told me about whiteboard.chat.
Infinitely Teaching 
Thank you so much for making me aware of whiteboard.chat! I teach college math, and during the pandemic had started using the Microsoft Whiteboard app to get student involvement and monitor/give-feedback to their work during problem-solving sessions in class, but it ended up being way too much of a resource hog. Then I came across whiteboard.fi, and it looked like the perfect solution, so much so that I ended up getting a subscription ($18/mo, gulp). But I’ve had connectivity issues and my students complain of sensitivity to their styluses – maybe that’s the lagging issue you describe? Now, whiteboard.chat looks to be even more powerful than whiteboard.fi – and it’s free! So far no responsiveness issues, knock on wood. Amazing!
Fantastic! I’m so glad it working for you!