At this point, I’ve taken gear to and from DR, Mexico, Costa Rica, and Colombia. Always in checked luggage, with little to no opsec. The only time I got any hassle was going from Guatemala (it was a connecting flight from Costa Rica) to Cancun airport, where I was pulled aside and had my bag checked. But I told him what it was and he didn’t care, he was just making sure the syringes weren’t for heroin.
Basically anytime you go from a seedier country to a nice one, you might get pulled aside if you’re alone. Funnily enough, I was pulled aside after coming back to NY from Colombia and the cop who went through my stuff didn’t even acknowledge the vials.