I have a Bell Z20 Mips. To be frank, I don't understand why this helmet is $200. It's fine - I wouldn't describe it as heavy but it's also not feather weight. Bell lists it as 310g. Ventilation? Adequate... not great but not bad. Pretty much like every other bike helmet I've ever owned. I mainly bought the Z20 because it fit well and I liked the way it looked. The LBS had a cheaper Bell helmet that also fit the same, but I didn't like the color, so... yeah, I spent extra because I liked the way it looked.
I have a helmet from another manufacturer that is 276g and can assure you that the extra 34g on the Bell is not noticeable. Unless you're a true weight weenie this seems like a non-factor.
In terms of safety - All Bell helmets meet the same CPSC certification standard, and they all use the same or similar retention systems. Bell has a $65 MIPS helmet on their website that is just 15g heavier than the Z20 and I suspect the only measurable difference is the appearance and colors.