In California, a flashing forward facing light and flashing rear light are legal and the cops will never, ever stop you for using them.
I use them all the time and the forward facing one is probably more useful, simply because people don't look for cyclists, only cars. Cagers see it when turning from a side street- they can be looking directly at you, and never see you or even in their mirrors so they don't cut you off. IMO, a flashing forward light is a great safety tool.
Nowadays, people are used to looking at DRL's all the time.
Rear lights are ok but my feeling is that if they are looking at their phone, doesn't matter if you have a 10k spotlight, they aren't looking. At all. But, maybe they will see it in their periphery and wake up.
I use both front and rear flashing lights. I think it helps quite a bit.