I doubt its double glass on the Apogee (I used to have a U16M also; nice camera but slow downloads and very slow to cool otherwise a very good unit). Both have argon which is even in the Starlight Express Trius range now.
The latest offering from Apogee is the Aspen model. Not sure what the differences are but the high cooling option cools even harder than a FLI.
It probably takes half an hour or more to get there though.
Doesn't sound like a problem but if you take twilight flats like I do and leave it to the last second to take them you are blocked as the camera takes ages to reach the temp and by then its dark. Happened to me several times.
The worst was a power drop out at 2am and then it wanted to warm up then cool back down taking something like an hour - that's just stupid.
The theory is the slow cooldown takes thermal stress off the sensor so it lasts longer. The reality is noone experiences cracked/failed sensors from thermal stress that I have ever heard of so its solving a problem that does not exist.
Not really a problem if you are using it in a remote situation and power up in plenty of advance time. Its also a bit slimmer than the Proline and a little bit lighter although the heavy cooling unit may not be. I like the colour of the Apogees
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Greg.