Do you consider it safe or wise to buy one online with a credit card?
Obviously best is cash at a gun show with no paperwork.
I would consider someone selling FRTs or Binary Triggers for cash at a gun store more likely to be a Fed than any storefront. Orat least sharing info with them. That's like the guy at your shooting club that's always talking about kidnapping the Michigan Governor; just too juicy a target.
What is your appetite for financial risk? Like I said, I'm pretty sure no one has been arrested, and the folks that were contacted were asked to turn them in or destroy them, so worst case, you may have to lose your $300 trigger, but it's very unlikely simply ordering one online will lead to a raid and your dogs shot.
I ordered mine from BDU, but like I said, I was more making a point. If they win in court and come to my door, they can have it, still in it's package. But as long as it's legal, I have one.