How to achieve this effect with Screenflow

Kh 

You can get pretty close.
Select your video
Under Reflection (you don't even need to enabling it as you don't actually want a reflection) turn up Corner Round to 400
Go to cropping and crop Left and Right and you should get close to a circle.

webcam set to 1280x720

Kh We want to make this easier though of course.
Fill out the form and make the feature request so we can build this in as an effect. Developers are interesting in hearing interest in this.

ScreenFlow Feature Request Form

This is all well and good, but it baffles me how, after 10 major versions, ScreenFlow is still so bad at this. Why do you have to get pretty close? Why can't you just have it with a couple of simple clicks? Is it hard for computers to draw circles? Before I bumped into this post, I was just trying myself, and the first order of frustrations (you get exposed to multiple levels throughout the process) came from the inability to have the size of the clip in pixels clearly displayed. One has to google around their camera specs first, and then just start doing the math 🤯 And that's not all, because now you have to manually shift the left, right, top and bottom margins to square up the picture. You can get pretty close, but why? A rhomboid is not a circle (check the screenshot you posted above, please). And god bless you don't decide you have to reframe the picture, like I hope you get it right the first shot, otherwise you'll need to tweak them all four again and again. I don't understand why it can't be simpler, like pick a shape, stretch it to fit the bounds of the clip the way you like, click ok. You want a border? Check a box. Reset? Click the button. It looks like it is designed to make it hard, like seriously: could it be any harder than that and how? Also, your developers might be interested in hearing requests like this, however... will they ever act on those requests? It looks to me like more than 3 years went by already...