I've never had anything super fancy, but it seems like the biggest change for feeling visible for me was putting additional flashers on my helmet and then running them during the day. I suppose putting lights up above the hoods of most vehicles that can be seen through other car windows.

Although your question was specifically about a rear light, I just want to mention that after 30 years of bike commuting i traffic I cannot overstate the importance of a mirror or mirrors (the glasses-mount Take-A-Look is my favorite) and AirZound Air Horn (or similar).

See. Be Seen. Be Heard.