Putting these here so I don’t forget, and someone else can take advantage of a full lazy couch day of smart brake light research:
Battery: 400 mAh li-ion
Size: 50mm L x 34mm dia
Weight: ~40g
Water resistance: IPX6
Mount: screw mount back
Input: DC5V 300mA
Light: 50 lumens max
Charge: USB Micro
Cost: (Nov 2021) around $15 on ebay or $23 on aliexpress
Same as above, but comes in a 2 pack with dedicated baseplate mounting bracket(s)
Cost: $40 on backfireboardsusa.com or ebay
Enfitnix Xlite200 now with carbon fiber oOh
Battery: 400 mAh li-ion
Size: 31mm L x 34.5mm dia
Weight: ~30g
Water resistance: IPX6
Mount: quick release
Input: DC5V 300mA
Light: 30 lumens
Charge: USB C
Cost: $30 on amazon, ebay, aliexpress, etc
Battery: 500 mAh li-ion
Size: 44mm L x 34mm dia
Weight: ~56g
Water resistance: IPX6
Mount: screw mount back
Light: 100 lumens max
Charge: USB Micro
Cost: $12 aliexpress, $15 on ebay
Oil-slick and pink colorways available for you fashionable bros
Meroca Super One
Battery: 500 mAh li-ion
Size: 44mm L x 34mm dia
Weight: ~56g
Water resistance: IPX6
Mount: screw mount back
Light: 80 lumens max
Charge: USB Micro
Cost: $14 on aliexpress
Rockbros Q1
Battery: 300 mAh li-ion
Size: 40mm L x 34mm dia
Weight: ~30g
Water resistance: IPX5
Mount: quick release
Light: ?
Charge: USB Micro
Cost: $14 on aliexpress
Battery: 300 mAh li-ion
Size: 40mm L x 34mm dia
Weight: ~33g
Water resistance: IP65
Mount: quick release
Light: ?
Charge: USB Micro
Cost: $16 on aliexpress
Rockbros Q5
Battery: 400 mAh li-ion
Size: 40mm L x 34mm dia
Weight: ~55g
Water resistance: IP65
Mount: screw mount back
Light: 60 lumens
Charge: USB Micro
Cost: $20 on aliexpress or ebay