I just received a Therion yesterday and for me, its a great mod with some big caveats depending on the intended user.
TL;DR> I would choose the DUO over the Therion
# Long Version
1. There is no battery gains with the Dual (Ok, maybe a small amount... I'm running it in single 18650). What this means is that the battery life is not great, combined with the 87% efficiency rating of the chip make for a device that is not great for batt life. That said, on board charging, 18650 (can carry spares) and for me, I run in single right now and it is not horrible...
2. The DNA75 chip is NOT the same as the DNA 200 chip. I have 3 other mods with DNA 200 chips and all of them out perform the 75 thus far. Even using a low Watt setting (for me) of 55W, you can sometimes get a "device too hot" warning. The board temp comparisons that I have noted are about 15-20 degrees warmer on the DNA 75 vs the same atty/same watt settings on a DNA 200.
@Wingsfan0310 mentioned heat and how that is the enemy of electronics. My testing of this is absolutely bang on to electronics theory. There's just not a lot oh headroom from 55W to the max of 75W, combined with the smaller enclosure... Additionally, there's no venting on the Therion. Looks great, but not great for heat dissipation.
3. 510 connector. Now, I have found that some of my atties have 510 pins that are just a tad too long for the device to sit flush. You can screw it down till flush, however it may short or read low ohms. At first I thought I had a bad unit but when I compare the atties that work vs those that have issues, its apparent that the atties with the hybrid/standard length cause the prob. This indicates that the 510 may not have a wide range of tolerance as other mods. I have the Triade and the 510 on it is superb! (Please note, I may have a faulty unit... still looking to isolate... but this is just my experience with my device).
You would think with all that I posted above, I feel negative about the Therion. I actually do not. I love it for "what it is". I also have 7 other mods that I regularly use. If this was my "only" mod purchase or it were purchased to be "my" only or main device, I would not pick it as the battery life is not fantastic and the style of which I vape is at the top end of what this device can reliably do. If I vaped TC 400-450 deg at 45 watts... This device would be great... in its current config, its just not versatile enough to be "my" main device or go to "rock star" device.
These are just my opinions and my experience with the device for a little over 24hrs.
I hope this helps any!