Hi Nedus Mustafus
Well...I'm going to try to address this point by point.
Good ol' RF. I knew you'd show up eventually.
The first and most important point is your concern with stacking batteries. I'll not imply your concern is unfounded, because it certainly is. The design of the REO allows for heat & gasses to vent unhindered, meaning there is no pressure buildup in the device itself when a battery fails, therefore the device won't explode. And batteries fail, even when they are not stacked not often...but it does happen.
I knew Robert wouldn't produce something unsafe, but thank you for alleviating my fears!
In the case of a short circuit, the nice thing about the REO is that as long as your spring isn't over compressed, it will collapse in the event of a battery overheating...stopping the short circuit from continuing to damage the battery or device. The electronics on the VV version also recognize a runaway situation and will shut off.
So how exactly does one determine if their spring is "over compressed?" Mine still looks the same as the day I bought it, as far as I can tell, but it never hurts to be sure, does it?
Having a catch cup full of juice all the time would be an annoyance for me too, really...I don't tolerate that kind of mess for long. If you are finding this to be an unending source of annoyance, you may want to try a cartomizer instead of the 306. While I love my atties, I admit that there is a definite advantage to the carto as it holds onto more juice...lessening the concern of spilling juice. My guess is that you are indeed over juicing your atty...there should hardly be any juice in the cup most of the time. I am guilty of over juicing occasionally, but not often enough to bother me.
I think the 306 has ruined me... I vape, and vape, and vape, and vape... I'm sure it's user-error more than the fault of the device, but it's just something I've learned to live with. I don't think correcting my habits would be very easy.
You may also be experiencing what we call auto-feeding...where juice tends to just keep coming, keeping the catch cup full all the time. This can happen as a result of several things. The cap on the bottle can be on too tight or too lose, the atty being used could be partially clogged or the temperature could be elevated so that the bottle is under more pressure than it normally would be. I have a mini that auto feeds all the time...but it's due to me running my atties for too long between cleanings and me having my mini in the car when it gets hot. If auto-feeding is occurring, you can try cleaning your atties and/or possibly drilling out the holes on the sides, you can adjust the tightness of the cap...and worst case you could try installing the reducer tube that came with your mod...if you bought it new. The reducer tube (pictured below) just needs to be inserted in the bottom of the feed tube. You don't need to use the whole piece and you don't need to insert it very far. It restricts the flow of juice more so that auto feeding doesn't happen.
Yes, I'm familiar with the reducer tube. I'm the original owner of my "beat-up, but still beautiful to me" Reo, and I tried the reducer tube out when it initially came in the mail, but it made it too difficult to feed juice into the atty for me. I kept getting dry hits with it installed. As far as I know, I don't think the Reo auto-feeds, but I do draw rather hard in order to keep juice in the 306. The thing is awfully finicky if it isn't nicely saturated.
Honestly...if none of these suggestions help, I would recommend getting a hold of the shop and sending it in for a once over. It's not supposed to behave that way. One of the reason's Rob designed these the way he did is because he HATES juice spills and leaks with a purple passion.
Like I said above, I think it's my fault and not a problem with the unit, but I could be wrong. I recall the same thing happening with my Mini, even after I sent it to the shop, so that leads me to believe I over-squonk quite often.
Now as to your last statement...I don't know that I can even start to try to justify one device over the other. Both are good devices. We have a Provari here at the house, and it's a cool device. For me, I adore the juice feeding aspect. I hate dripping and filling cartos...always have. That's why I found the bottom feeders suit my needs better. The REOs make it easy for me as I have had very few issues that weren't easily solved by myself....most of my issues were usually user error anyway. Tanks satisfy the problem of dripping & topping off for most people, but I still find them to be a hassle for me. And the most important aspect to my success as a vaper was that it needed to be easier than smoking. Check.
I too hate filling cartos. Syringes and I don't play well together. I know, I know, they make cool ones now that don't require syringes, but I've yet to try a carto that could match up with a Cisco 306. It's just the way it is for me. I've never tried a tank, but I've not heard very good things about them... they leak, they flood... i.e. they suck. I'll pass on that hassle. A full catch cup is a lot easier to deal with than 1/2 mL of juice spilling all over you when a tank seal fails!
So can I convince you? Probably not. Nor will I try. I think for now, the most important part (to me) is figuring out a way to help you find resolution to your issue with the full catch cup. And I really mean it....if it's not something that can be easily resolved on your end, then it should get a once over by the shop to make sure everything is good. Whatever you end up deciding...all that matters is that it's working for you and you're cravings are kept at bay.
Can you convince me? You'd be surprised. Females just seem to have a way with me... I think I need to chill on the squonking... possibly changing to the new tube/bottle would help. I hate to take this tube off as long as it's working correctly. If it ain't broke, don't fix it, right? Bear in mind, the tube in my Reo is ripped rather severely on the end that sticks down into the tube. You also helped me with that issue many, many months ago.
So now before I post the pictures (mentioned above) I just want to let you know...that I am moving this discussion to its own thread so it doesn't get lost in this one. I think this merits further participation and discussion. I'll send you a PM with a link so you know where your post went.
Thanks for looking out for me!
I have to type something here so ECF will allow me to post...
I remember that 
