I'm a big fan of the Ravx Super Sight and use it during the daytime. It takes two AA's and has four different blink-modes. I get compliments (and some complaints from exploitative wheelsuckers) on it all the time.
Whenever I check out my profile's reflection in shop windows (silly, vain creature, I freely admit this) I'm always pleased at how bright & visible it is.
Plus it's quite lightweight & aero!

I bought this, thinking it would make the perfect rear light - dynamo power + battery backup right? It didn't work that way, so I replaced it with a regular dynamo light.

I think the problem was that unlike a regular dynamo light, you still had to turn the rear light on and off with it's own switch. It might have been a relatively small thing, but that was one of the advantages of a dynamo light - I turned the front light on and the rear light turned on automatically. More convenient, didn't forget to turn the rear light on, and I could turn the rear light on while riding.

Just to illustrate what I mentioned above, the OP has this...





and is thinking of adding something like this (NR Cherry Bomb) in order to boost off-axis visibility:


I'm all for having secondary lights to provide redunancy, but a DiNotte 140 is a tough act to follow