Seems like the main flaw in the ones the author labeled "awful" was a geofence policy that limited the top speed on a "bike path", or locked them out of it altogether. Makes it a bit difficult to generalize their conclusions, especially without knowing more about the path to be able to judge whether that policy is reasonable (and/or mandated by the city).
The Venice beach bike path is a "standard" mixed-use path. Wide enough for bikes to pass in opposite directions - total width is a bit wider than a full size pick-up truck. It's fairly twisty and bordered by sand on both sides, so if you run over the edge, you probably fall on your face.
As for appropriate speeds, a jog is about 5mph. That sounds reasonable and safe for a small-wheeled scooter. A townie/cruiser bicycle will do 10mph without too much effort, so that could be the upper bound too. Much faster with those small wheels seems dangerous regardless of location.
