Tesla Two Sub Box owner here. I had a look at the GX-200 as well, they're a little bit different in terms of mods but the same in the way they are unregulated but not truly 'mechanical'.
Tesla has two built in 19500s lions in parallel for a total for 40A and 4000mAh so the size of the thing is very small - as compared to removable 2 x removable 18650s.
Both have:
- Short circuit and reverse battery protection (obviously the Tesla reverse battery protection assumes that they instert the batteries correctly during production!)
- Tesla has a 15 sec firing cutoff and I think the GX-200 has 10 sec limit from memory
- Low voltage protection - neither will fire below 3.2v
Tesla has a 40A max output DOVPO has 20A max with over current protection that kicks in at 30A
Tesla fires down to 1 ohm vs 2 ohm on the DOVPO
Tesla charges at 1A max via micro usb vs DOVPO 800mAh max (it takes 3.5hours to charge the Tesla) but the advantage of the removable 18650's is you can have two fresh ones charged on your external charger and ready to switch out.
Tesla has spring loaded 510 vs a user adjustable 510 on the GX-200
Regarding the Tesla, I wasn't keen on buying a mod with built-in batteries - I saw it as a con in my book - but when I saw how small it was I just thought f@#% it - for the price I'll give it a go. I love it. I've been using it daily for a month. The only time I put it down and pick up my brass 4Nine is to charge it. Hits almost the same too - I mean it hits like a champ - but the 4Nine in 18490 mode has a slight edge - it's a hybrid after all - however - the battery life on this thing is stellar so the battery sag is nowhere near as noticeable as the 4Nine. If I'm at 4.2v at 9am, I'll vape right through until the next day to about midday before the fire button goes from blue to red (3.6v indication) and I barely notice any reduction in vape consistency until i hit the 3.6v mark and then I charge. I'm chain
vaping at 0.6ohm and minus eight hours sleep so that's about 15hours of decent vape time.
Here's a thread I started when I was still deciding:
Tesla Two Box Mod - yay or nay? | E-Cigarette Forum
I've got another on the way so I'll have one fully charged at all times. Button is one of the best I've used on a mod - nice and clicky. Build quality is great and all my attys sit flush. Don't over tighten your attys on the 510.