Extremely fine haze, it's the only fluid that I tested that starts unnoticed on any machine, even on the cheaper hazers. I've even used it in restaurants without bothering anyone. Beams come alive without bloating the atmosphere (especially important nowadays that people get uncomfortable when they see a foggy venue).
On one of my cheaper machines, it always starts with a slight, sweet smell, which disappears in a minute, though I haven't noticed it in my Unique. It's definitely not uncomfortable though.
It's absolutely not efficient, and usually requires 2x or 3 times the output setting on hazers, so I wouldn't use it in bigger/outdoor events, but it works wonders even in the 1000+ people nightclub it's regularly used in.
I've used it on many machines daily for more than a year (including a Cameo Instant Hazer 1500T Pro and a Look Unique 2.1) without issues.
Definitely recommended!