Copper can indeed be toxic the symptoms closely resembling that of arsenic poisoning. For that matter the manganese often used to lower the need for nickel and the chromium in stainless steel can be as well.
The nickel both electroplated on the copper tip and as a component stainless steel tips can be carcinogenic.
Before anyone goes looking for 24kt gold drip tips it may be wise to put things in perspective, the water you drink in just about anything has traveled through copper pipes and the dissolved copper would be a much higher dose then that you would get from extended use off a drip tip.
Some people have a strong allergic reaction to nickel and that certainly could cause irritation to the lips. But as far as exposure to toxic levels of theses metals it is a non issue.
To err on the side of overly cautious all these mouth parts including carts should be made of SAE grade 440 stainless steel often referred to as as surgical stainless steel.
Really given that allot of the items come from China a country notorious for using sub standard material and the fact that there is no regulatory body overseeing the manufacturing. I would be happy if there's no lead in the paint and I don't find a dead cockroach in my 30 ml bottle of
juice. Even if that was the case I think you would still be worse off lighting a analog