I think the tool widget is an awesome addition. I have no qualms about this feature whatsoever. My only suggestion for an implementation change is to avoid bouncing UI features around by showing the Corner Radius and Thickness boxes greyed out underneath their respective checkmarks. Then only enable them when the options are ticked. UI elements appearing and disappearing, especially when not at the end of a list, are kind of jarring. Otherwise, super cool and great work.
Now, less excitedly, regarding the merging of multiple tools:
Pros include...
...better discoverability of tool options. That tiny down arrow next to a tool is not a great indicator that there are more ways to create similar geometry.
...a cleaner interface. Less buttons, so you click the thing you want to make and then are presented with the options that are relevant. Makes sense to me.
...better integration of features in the future. Any Sketcher features implemented that apply to Rectangles should be available and well-integrated with every version/mode of Rectangle; merging the tools would make this pretty much mandatory.
But! One major con to merging the tools: This could mess with shortcuts/workflow in a big way.
For some shortcuts, it won't really matter too much. Arc is a great example, as there are only two options. The shortcut for Create Arc remains GA just as it has been. The shortcut for Create Arc from 3 Points would effectively be GAM. A perfectly fine shortcut, just three taps. This will be true as long as every time a tool is selected, the settings begin at some kind of default. Just because I used Arc from 3 Points last doesn't mean that GA should now be Arc from 3 Points. GA should still be Create Arc, and GAM should still be Arc from 3 Points. This is absolutely vital for keyboard muscle memory.
Arc is fine in this regard but rectangle is a different story because there are so many options. I have all three versions of the rectangle tool set to two-key shortcuts. RR (reg rectangle), RF (rectangle filleted), RC (rectangle from center). Two keys each, no modes, no looking over to a widget to confirm my settings are correct. Just tap-tap and then click to place. The amount of times I would have to hit M to get to these on a regular basis (especially for the number of options for rectangles in particular) might just drive me insane. Maybe the separate tools that exist right now can continue to exist
at least within the keyboard shortcut customizer. Instead of activating their own separate tool, that shortcut would just launch the new merged tool with that option already selected. If the separate keyboard shortcuts remained an option, then using the most recent mode/settings of a tool would be acceptable. Just as long as there is
some infinitely repeatable keyboard-accessible way to get to these specific tools that are being "merged away," I'm cool adapting.
Additionally, M is not an ideal mode switching key as it requires leaving home row with the non-mousing hand. If this is going to be such an important and oft-used shortcut after the merge, it would be awesome if it was customizable. Probably a conversation for a different thread, though.
My two cents, anyway. Keep chugging along, I'm really looking forward all this work being pulled in!