I enjoy this discussion between these 2 lights. If you have both I would like to hear from you. Again do you guys want me to compare these two in a video or just pictures and type out here?
Both the D4 and the FW3A are great lights. They're both very small and compact for 18650s.
Comparing the stock D4 to the stock FW3A here are some advantages and disadvantages of each:
Emisar D4
+ Better heatsinking
+ Bigger selection of body colors, textures and materials, and LEDs.
+ Higher output due to extra LED
+ Sideswitch provides a more secure grip when using light's controls.
+ Multiple battery tube configurations
+ Mechanical tailcap lockout + electronic lockout.
+ Antiroll design even when clip is not installed.
+ Lexel aux LED board available now.
- Protruding sideswitch makes the D4 prone to accidental pocket activation. Can burn a hole through your pants if not locked out (this happened to 2 of my pants pockets... oops!)
- Locking out a light to prevent accidental activation removes much of the convenience of having a pocket EDC.
- RampingIOS electronic lockout is 6 clicks
FW3A
+Elegant design
+Metal tailcap switch should last longer than typical rubber boot. The D4's button boot can wear out.
+Tailcap switches tend to be more resistant to accidental pocket activation than the D4's protruding sideswitch.
+ Anduril firmware has many more features than RampingIOS.
+ FW3A has a triple-channel FET+8+1 driver. This provides much more regulation than the D4's dual-channel FET+1 driver.
+ Default top of ramp is set at 8x7135 (2.8 amps)... bright, but not bright enough to burn a hole in your pants pocket. Even if the light accidentally turns on in the pocket from the button being held down by your pocket stuffing it probably won't destroy anything, unlike the D4.
+ weighs less than a D4 with 18650 tube.
+ Narrower, which may be better for EDC pocket carry.
+ Anduril's electronic lockout is 4 clicks.
+ Lexel aux LED board in design phase, but not available yet.
- No mechanical lockout possible. Electronic lockout only.
Of course the above just refers to the lights in their stock configurations. Both lights can be modded and the issue with the D4 accidentally activating in the pocket can be solved.
The FW3A is much newer so fewer options are currently available for it. There is a possibility that other versions of the FW3A will come out. Neal (distributor of the FW3A) mentioned that he would check into the possibility of copper and titanium FW3As.