Willit Run,
Biggest down side we've heard of the Zulu is the size and discomfort to some. Depends on the person, though. I have found them much quieter than any other headset, also. Last time I checked, it wasn't TSO'd, either (not that I personally think it matters and is not a factor outside the U.S.).
Window heat interference is a rare problem, but is usually an aircraft issue more than the headset.
Folks that have the earbuds with our product, either don't use it (it's a stupid requirement by the FAA), or just put an earbud in the earcup... they don't actually stick it in their ear(s).
Vast majority of our customers put Telex last for about everything except the "earspike" type headsets like the Plantronics MS50 and Telex Pro 5x5. They will actually damage your hearing. Consider the cockpit db of a Boeing is typically 82-86 db (extended exposure to 85 db will cause hearing damage). Now, to hear over that 82-86 db, you have to turn up a single earpiece headset to some level above 82-86 db, so the hearing damage is worse in the ear with the earspike.
IMO, wear a dual earpiece headset, regardless of what you choose you'll be better off. Everybody is different about what is important to them, so there really is no ideal headset... all depends on the person.
Mike