Naively, I would expect that a high racer is safer in traffic than a low racer. With the rider higher up, she or he should be more visible compared to being closer to the ground. Considering that safety in traffic is the main reason holding me off from riding a recumbent, I wonder: is there evidence that a high racer is safer than a low racer, considering visibility in traffic?
In my experience, a higher bike will be seen easier and sooner than a lower bike.
I have had multiple riding events where I've been blocked or obscured by vehicles so another road user (driver) makes decisions based on what they know and what they can see. If you've not been seen, you're not part of their decision.
Likewise, being lower provides a worse view, and therefore less information on the surroundings for the rider. I've had one night ride on my mid-height bent where it was also foggy, and could not see the road surface before it passed out of sight below my bottom bracket (front bracket?) I ended up riding off the road into the gravel because the edge of the sealed road was not visible.
On the flip side, I have a strong but unsupported belief that once my recumbent has been seen, the observer is much more likely to notice me and change their actions if required.
The human brain has "layers" that roughly correlate to the embryo's stages of development. For simplicity, the "reptilian" brain deals with autonomous stuff like balancing, walking, breathing, etc, while the "simian" brain is under willful control where you start thinking about breathing etc.
A road user while driving might observe a regular cyclist, and that information might never rise above the reptile level of brain. The reaction is autonomous and doesn't bother the active thinking processes.
Observing a weird bike immediately kicks the thought up to management layers, where the simian brain has more of a reaction in the conscious space.
tl;dr the lower the bike, the harder to see but once its been seen you're more likely to be considered by a driver.
I would not use a recumbent for primarily Central Business District (CBD, urban) riding. My commute is basically 50% rural farmland, 30% residential, 10% park, and 5% dense city so I can ride 30+ minutes without stopping. Recumbents like to just keep going, and a city environment doesn't encourage that at all with traffic controls and pedestrians. Dooring near-misses tend to be more common when I'm on the recumbent too, but that may be observer bias (I ride the bent 95% of the time now.)