I bought the "Brake Free" (the one that was on Shark Tank). I thought it was silly when I first saw it on the program, but then I saw a rider that had one on in sunrise/sunset and it really caught my attention. Especially since typically the helmet is right in your eye-line.
It has several settings. I have mine run all lights dim, the middle sections light up bright while braking, and a hard stop all lights rapidly flash bright. Completely forget it is there, it holds a charge for several months for me (that probably translates into 10+ hours of riding). It auto turns off and when you pick it up it turns back on. You can follow the link below if you want more information. Highly recommend, even though it is pricey. Seems well built, it mounts cleanly to your helmet (it can slide off and on if you have multiple). It says water resistant, but I have been in a downpour and it didn't miss a beat.
https://www.brakefreetech.com/collections/brake-free-products/products/brake-free
Ryan