They are oval to provide a place to mount the hose. A round shoe would be larger and still not solve the problem if you're mounting the hose in the usual manner.
I sometimes need to clear obstacles so a fixed-height shoe wouldn't be a good solution. With some types of work (like small thick material) my brush is doing more dust-containment than dust-extraction For sheet goods having consistent brush contact may have advantages.2) It seems most shoes are attached to the Z axis. Some are fixed to the X axis and move with the router w/o vertical motion. It seems that being fixed to the Z axis will change the brush pressure as the DOC increases. Any issues with this? What are the pros and cons of the two?
Ideal situation is one quickly detachable system of each type ? I don't any examples of that to offer. The video under "Similar Threads" in your post is interesting.My immediate need is to mill flat stock mostly plywood so I'm leaning towards a fixed design where the bit retracts through a hole, but I'm open to suggestions.