I too use both....
Watch for the very obvious difference in cleanup later between the Zephyr, once it is dirty, and the Volcano (especially the EZ valve.)
Your summary is well thought out. Looking at your decision this might have been a post more helpful in the Zephyr thread.
You will see in the Zephyr thread, I love the Ion... and did a video etc.. and spoke VERY highly of the fact that it gets to temperature faster than the Volcano, and the bag blows up faster too...
So I used it more for a few days than the volcano, until I found the weak link, which was the non-removeable top which collects a good deal of resin.
Cleaning is not an impossible task, BUT.... the need to clean Zephyr comes after only a dozen sessions, as opposes to the Volcano EZ Valve which for me functioned daily for 3 years before I ventured to clean it, and found a great deal of buildup. The buildup was no problem, and obviously did not hamper function since it was out of sight and out of mind.
The cleanup of the EZ valve is at
http://fuckcombustion.com/threads/volcano.220/page-46#post-571059
with the Zephyr, in spite of enjoying it's speed and function more, after a dozen sessions the top screen was able to get gummed up with resin , due to very limited and shallow clearance between the top screen and the cone/nozzle that rises from the Unit.
Please do not construe this as a deal breaker.
I am just making you aware of one thing you may have overlooked.