I wasn't wearing my moderator hat when I wrote that I had on my retired Customs Inspector hat on.
The only delays that you might incur in Customs is if some young green shiney new Customs Officer who has no idea what the item is and thinks he's intercepted a major WMD shipment and slaps a hold on it while he contacts the ICE and ATF Agents who may or may not know what to do with it. If the ATF agent knows what it is and understands its exempt status he will tell Customs to send it on its way. Or he can say it needs an Import licesense. If he says that then you will you will have to follow the procedure I already outlined and apply for an ATF Form 6. During the two our three weeks it will take to get the response for ATF Imports your shipment will be placed in bonded storage, for which you pay a daily storage fee. When ATF issue the exemption letter or even a Form 6, you have to send of that to the Custom Office that detained your shipment and they will review it and and notify you of the stoarge charges that are due.
Most likely you shipment will come sailing right on through, not a probelm.
But ask your self who do realy want to get your advice from about importing articles, the sales man or the Customs Officer.
I based my response on my experience from being on both sides of the importation desk. Do you want to hear my story about the time I imported an antique rifle from Australia and spent 8 hours sitting in the Customs waiting room while the young green shiney new Customs Officer who has no idea how to process an import of an antique rifle. He was really embarassed when he found out he shouldn't have siezed the rifle and that I was a Customs Officer and didn't tell him.
Oh and by the way shipping in two boxes will cost more and send up red flags if Customs finds one