Stopped by this thread because I've been thinking of getting one of these myself and I use the same gear you have.
If you like the way your Naut Mini hits when it is at 4.2v, i would consider the ego one as a backup or around town device. Soon after I started vaping (six weeks ago) with an Aspire CF Sub O, (which is also a constant 4.2v, like the ego one) an Atlantus and a nautilus mini, I picked up an iStick 10 from a B&M shop in town as a backup. (By the way everyone, if you're in NYC, go to one of the few dedicated Vape shops around - the head shop/ smoke shops are ripoffs). It is a device that is almost great. I dig the size and form factor and I understand that battery won't last all day. I've got a naut mini on it right now as I type away. I then ordered the iStick 30w as a way to push the Naut Mini as well as dial back the Atlantis, which was too much for me at the time.
One thing I've noticed as I adjust to vaping is that my tastes and needs have shifted. At first, sub-ohmming was way too crazy for me until I learned to not suck on it like a cigarette on a cold day. Then I was rocking it for a while (so I bought a SubTank Mini to avoid Aspire coils and start playing with rebuilding). This past week, I've been all over the naut mini and brought the little 10w back into rotation. I mention all of this because even though a .5 coil at 4.2v (which is somewhere in the lower 30s for wattage, I think) does not sound like your cup of tea today, you may want to explore it sometime soon. Until then, you've got a nice little battery (you said that small form was important). You might find that the atomizer that comes with it finds new life on your iStick with either the .5 or the 1.0 coil. Even if it isn't your go-to rig, it's always nice to have a backup as you're getting off cigs.
Two other options for small rigs (I'm sure there are more):
-the iStick 10. It might not get you enough throat hit, the threads are brass instead of SS, and the circuitry is B-grade, but it's small and light and cheap (about 2 or three days of smoking sort of cheap). If your current iStick and Naut Mini satisfy at 10w, then this might work.
-the ego eGrip. 20w variable, built in tank. Pretty good reviews (with a few issues, of courses).
Good luck and please post what you end up getting and how it worked out for you. I'm looking for a good pocket vape setup.
I couldnt hold myself any longer and bought a EGOone today.

I have been using for couple hours now. My experience so far:
- Amazing size
- Flavour is much better in EGOone
- Since throat hit is what I seek I didnt even open the .5 coil
- Even with 1.0ohm coil with tight draw its 40-50% less throat hit compared to iStick30+NautliusMini (13W - 1.8ohm - smallest airflow). Not to mention the EGOone's battery is nearly-full and throat hit is going to decrease gradually...
So the answer for this threads question is NO...
NautliusMini is just perfect. I just need to find a smaller battery that can go up to 13-14W