I'm not a chemical engineer, but I can pretend to be a rocket surgeon...
(Background - feel free to skip) I love cinnamon based e-liquid, but no one mentioned to me that it would melt polycarbonate and acrylic; I found out the hard way. The first thing that melted was the drip tip on a clearo. I got a stainless steel tip, but I also got a vivi mini nova in the same order, so I didn't use the clearo. After about 3-4 weeks, I noticed that the threads on the top of the nova tube were melting. It wasn't until I took a picture, so I could post and ask a question about it, that I really saw how damaged the tube was:
A very kind ECF member walked me through how to put together a glass carto tank, but since I was waiting for it to come in the mail and had nothing else, I decided to keep using the nova - I couldn't break it more, right? That only lasted a couple of hours. Nothing bad happened, it just occurred to me that what the plastic was
breaking down to (insert correct technical term), might not be the best thing to inhale. I got a little nervous. I switched to clearos and less aggressive juices waiting for my tank to arrive.
I thought I was home free with glass, until about a week later, when the pretty acrylic caps turned to mush:

(L-new/R-mush)
I ultimately ended up using glass tanks with stainless steel caps, polypropylene tanks with silicone grommets, and stainless steel or glass drip tips. Sorry to be long winded, but I love typing about myself...
I'm not terribly picky about "safety." My cat walks on the counter and I'll share an ice cream cone with my dog, but the etching of the plastic concerns me. Think about beach and ammonia. Each are fine by themselves, but when they mix you have a problem. Polycarbonate and acrylic are fine, cinnamon is fine, but what is released when they mix together and melt? Just my
ETA: I should clarify that it was the same juice that damaged the gear, but the results were different. On the nova, the threads around where the top cap screwed on started coming off, like fine hairs. I guess I should have written "degraded" rather the "melted." When the juice was removed and the nova sat for a few days, it was very stiff and would probably crack if squeezed. The acrylic caps, on the other hand, really did melt. They got soft and sticky, and remained sticky even after being rinsed under the sink.