I've done these mods on 2 bikes I've owned.
Here's my recommendations:
Brake Light Modulators: Hyper lites.
https://www.hyperlites.com/unikits.html
these are very easy to install, especially if you use their license plate bracket thing. The wiring is very simplistic, I choose the option of 5 second flashing then steady as opposed to constant flashing. If you're worried someone isn't seeing you as they approach, release brake and re apply and they flash 5 secs again.
these also are a million times easier to install then "back off" modulators, which have to be spliced into the wiring harness, sometimes entailing cutting up the harness to find where the front and rear brakes merge, so both brakes activate the unit.
HeadLight Modulator:
https://www.comagination.com/
these work great and are plug and play, no wire splicing etc. they are activated when you put your brights on, and off when the brights are off. They are also ofcourse off when it's so dark out the sensor doesn't allow them to work.
t of advice, when you are approaching heavy traffic, turn them on 'before' you get there. Some people think headlight modulators inadvertently signal "go ahead" to other drivers. I found after 10k or more miles of use, that only happens if you turn them on right at the second someone is looking to make a left in front of you, or pull out on you. In other words dont wait till the last second to use them, you want to be noticed wayyyyyyyyy before the last second.
After having these I wouldn't own a bike without them, they definately help in being noticed. With the brake light modulators you'll find some people will even stop a couple car lengths behind you
edit to add: federal law, allowing headlight modulation, supercedes all local laws. ie they are perfectly legal.
regards,