I just am not willing to take any chances of having a product that could get me a visit.
I've had an active FFL license (of several flavors) off and on over the years.
For what I do now family and friends keep me busy and I don't have paperwork to worry about.
I can totally understand not wanting a government agent up your backside if your not used to it.
If I were you I would wright a letter to the appropriate alphabet soup and ask for clarification on your product.
I would clearly explain what was needed for the product to function as intended.
Make it clear you want a yes/no affirmation on if it is a tobacco product.
To me it is a reward/risk problem. In FFL stuff 10-20 years time can result from a common bookkeeping mistake.
For any unregulated/FDA laser you build the risks seem to be limited to (don't do stupid stuff in public or involving vehicles and you'll stay out of jail) or (law enforcement knows so little that unless you self incriminate your fine).
Or in other words it boils down to what johnny law can prove was your intent.
If your intent is offering an alternative way of using a regulated item in a less regulated way your in good shape.
Nobody throws a fit if you convert a rifle into a crossbow.
Is it still a regulated rifle? Sure is.
Does johnny law care that it can now shoot crossbow bolts? Nope
Would johnny law care that your ex-felon friend is shooting your rifle/crossbow even though he could buy a crossbow but the rifle is still considered a rifle and would be illegal for him to handle? (At this point you have to wonder what happened that the officer has gathered all this info)
I have employed an ex-felon as a computer tech in my FFL business in the past. Never had access to guns, ammo, powder etc, BATFE was fine with this. As part of the process local law enforcement got called by the feds. Since they know me they called me. Long story short the officer that came out BS'd with us about what the BATFE said as it was new to all involved and the officer than says that felon or not you can't work in this biz and not shoot once in a while. Says to my employee that if they were to ever need to shoot (testing) for some reason to just call the non-emergency number and they can send someone out to supervise.
For instance, I would have no problem offering 510 modules if I had the ability to make them. Any risk would be mitigated by taking the time to do an LLC and get an EIN. That way in a worst case they just take the biz assets (would be a liability case involving injury). If all your biz owns is a pile of 510 adapters your liability is pretty limited.
Realistically, you might get a cease and desist letter from the FDA if you were to ever get that much attention.
I actually think it a bit funny, being worried about an unregulated tobacco device part when just having a portable class IV laser could get you into more trouble.