You need no demo letter for making post samples as an 07FFL/SOT, but the requirements are slightly more strict and more costly for the manufacturers license. The ITAR fee alone just went to about $1750 per year. Add to that the $500/year SOT and the base 07, state and local business licenses and you're probably close to, if not well over $3000 per year. Additionally, you'll need proper zoning for light manufacturing, and yes BATF does check. Finally, as a manufacturer you will need to sell some items you make and show that you are engaged in a bonafide business requiring an 07/SOT otherwise your license will be pulled by BATF (at which point, you'll have to sell or destroy any post samples as noted above).
If you're thinking about getting an SOT as a means of expanding your personal collection, I would strongly advise against it.