I wanna bump this thread with a trick I just discovered on how to bring up old effects that are not in the current screenflow 10 list.
First, you need to go to screenflow 9. And save a preset only using the desired effect.
Then you need to bring screenflow 9 preferences into screenflow 10. (This way your preset migrates into 10)
By the way, to do the preferences migration thing, I will paste what I was told via email, this worked great:
1) Make sure ScreenFlow is not open. (save any work in progress)
2) Open a new Finder window.
3) Select the "GO" menu top of screen, Hold "Option" key with menu open, and select the "Library" that appears.
4) In the Library folder open Preferences folder.
5) Delete the "net.telestream.screenflow10.plist" file and rename your "net.telestream.screenflow9.plist" file "net.telestream.screenflow10.plist"
Now, your preset will show up in screenflow 10. You just gotta load the preset.
I know It's not very elegant solution of course but at least I can bring up mask to alpha now which was very much needed.