As I said, it may pass a casual inspection. Probably will even. And the further the observer and more fleeting the glance the better. However, in actual use it's not good cover IMO. Nobody uses an inhaler like folks use the Puffit. They don't look at it, play with it or wait. Take it out, pull the cap, shake it up (which 'never' happens with Puffit) and hit it right then. 10 seconds max. Puffit users stare into the hole waiting to the light then hit it for ten seconds or so straight, not two. It's gonna look odd to even the casual looker I think. In the same conditions I think palming the MFLB is much better cover for instance.
Yes, blue has advantages over black, but it's the way you use it not the color that's going to attract attention I think? Too bad your vape pen experience hasn't been more impressive to you, I assume that means you haven't tried Omicron or Revolution? While I agree they are stealthy in their own right, I was saying that open use blends in with the e-cig 'smokers'. I know guys here in California (where we treat smokers like fourth class citizens.....won't even let them ride at the back of the bus.....who join the guys at the bar out in the parking lot and toke up while guys a few feet away puff madly.
I just think counting on looking like a 'harmless inhaler' is dangerous false confidence. It will work most times, but has serious flaws in regular practice. Sooner or later it will lead to grief?
OF
I'd like to chime in on the stealth aspect.
Being in NYC, I've used this walking down the street and standing next to people waiting for trains (not in the subway) and have yet to have someone even look twice at what I'm doing. I completely understand that this does not function in a way a normal inhaler would and a seasoned inhaler vet would know that, but from my experience I don't think most people on the street do. Let's assume they do know exactly how an inhaler works ... I can't imagine a scenario where they are going to say anything to you or anyone else about what you are doing. Personally when I use this, I make an effort to look at comfortable / confident as possible. If I'm acting normal and calm the people around me have no reason to believe I'm doing anything wrong. Assuming that people know how the average inhaler works, how would they know that this isn't a new type of inhaler for a different purpose? It could be a new trial of a cigarette smoking cessation product, or a way to consume mint to clear phlem out of your lungs, etc. Again, I've personally found if I look / act like I'm doing nothing wrong, I don't draw attention to myself.
One time I went to a high profile building and forgot it was in my pocket and I had to clear a metal detector and put my pocket contents through an X-ray scanner. Tossed it on the scanner and walked through cool, calm and collected. The screener happened to have the device in his hand when I reached the other sice of the scanner. I asked what was up (staying completely calm. I hadnt done anything wrong and wasnt being accused of doing anything wrong. Plus, odds are the security screeners for the building are looking for bombs, guns, etc ... Not weed devices) I figured if he really questioned me I would tell him I used it to consume herbs to clear my lungs or something. He asked me "where's the spray?" I thought he was asking at the inhaler spray, but stayed calm and asked "what spray?" he was looking for pepper spray which I insisted I didnt have. I told him "that's not pepper spray, that's my inhaler." He very confidently (practically arrogantly, which was hilarious) insisted "I KNOW IT'S AN INHALER, WHERES YOUR PEPPER SPRAY?" I again insisted I didn't have pepper spray, citing that as a male born and raised in new York that would be out of character. He checked with the screener operating the x ray machine who clarified the person in front of me had the pepper spray.
Seconds later, my puffit and I were reunited.
TLDR: my experience is that if I act Like I'm doing nothing wrong, people around me look at me like I'm doing nothing wrong.
I'm not short, but I am built pretty petite.. I've been lurking the Pax thread and I'm still mostly leaning towards the PuffIt. 
