Users are complaining the the Speed Effect panel is confusing, so here's a patch to simplify it, by keeping all options visible, but disabling those invalid with the current selection.
This suggestion has been developed with @david mcsween (davidmcsween) on the basis of the work of Paulo José Oliveira Amaro: https://blender.community/c/rightclickselect/zfbbbc/.
It may be confusing to new users that Frame Number and Scale only produce a freeze frame unless animated, so I would suggest that the default setting is a check mark in the Speed checkbox and a value of 1. I'm not able to solve this myself, neither am I able to add much needed limits on the values in the value widget:
- When in Frame Number, then limit to number of frames of the current strip.
- When in Speed, limit to positive values.
- When in Scale limit to values between 0 and 1(or use a % scale of 1->100).