Here's the low down from a company that resells and manufactures laser systems.
All your lasers must be registered with the FDA! No exceptions. If you resell lasers the lasers must be registered with the FDA or have an accession number for import into the U.S. It doesn't cost anything other than time to register your systems. If you sell class IIIa systems they don't need to have any safety features. If you sell 3b or 4 you must have safety systems implemented per FDA.
If you build and sell a laser pointer you must meet FDA regulations:
21 CFR 1040.11(b) and 1040.11(c), limit surveying, leveling, and alignment, and demonstration laser products to Class IIIa.
Laser pointers are hand-held lasers that are promoted for pointing out objects or locations. Such laser products can meet one of two definitions for laser products. The first is for “surveying, leveling, and alignment laser products” as defined by Title 21 of the Code of Federal Regulations (CFR) Section 1040.10(b)(39):
“Surveying, leveling, or alignment laser product means a laser product manufactured, designed, intended or promoted for one or more of the following uses:
(i) Determining and delineating the form, extent, or position of a point, body, or area by taking angular measurement.
(ii) Positioning or adjusting parts in proper relation to one another.
(iii) Defining a plane, level, elevation, or straight line.”
Hand-held lasers promoted for entertainment purposes or amusement also meet the second definition, that of “demonstration laser products” as defined by 21 CFR 1040.10(b)(13):
“Demonstration laser product means a laser product manufactured, designed, intended, or promoted for purposes of demonstration, entertainment, advertising display, or artistic composition.”
If a laser product is promoted for pointing purposes, either of these definitions can apply.
It doesn't matter if you build lasers in your basement. If you construct lasers with the intent to distribute them you are a manufacturer and must meet manufacturer requirements. There seems to be an attitude that people are above the law or they are just small potatoes that the FDA will overlook. This is the wrong attitude. The FDA will mess you up if you pop up on their radar. Five years in jail is no fun. Neither is $250,000 in fines. Of course that's the maximum penalty. The minimum they will impose for non-registered laser sales is the immediate recall and destruction of all lasers systems sold and the refunding of all customer money.
You must follow the guidance of TITLE 21--FOOD AND DRUGS CHAPTER I--FOOD AND DRUG ADMINISTRATION DEPARTMENT OF HEALTH AND HUMAN SERVICES SUBCHAPTER J--RADIOLOGICAL HEALTH PART 1002 -- RECORDS AND REPORTS.
Kits are no exception. If your product emits radiation in its final form it falls under FDA regulation.
Finally, if you build lasers for your own personal enjoyment or amusement they do not fall under the jurisdiction of the FDA. Use of the laser system may fall under the laws of your state or local constabulary.