I have a whole stable of VV boxes---7 Madvapes VV boxes, Ken's family (Little Sister VV, 2 Big Brothers, and a Vari-Cool Big Daddy), a Big Splash with voltmeter from Shan, and a 3AA box evercool VV from Maximum Vapors.
A built-in voltage indicator is a very nice option. Sure, with most of my boxes, I can screw on the Madvapes Voltage Indicator (the one in the white or black case with 510 male and female connectors), which is nice because it reads the voltage both without and with a load, but that "solution" is slightly less than elegant, and it does take an extra 40 seconds to remove the carto, screw on the voltmeter, adjust voltage, remove the voltmeter, and screw the carto back on. Not that this is difficult, but---like any multi-step procedure involving threads and screwing stuff off and on---it can be slightly aggravating the hundredth time.
I like Shan's Big Splash with the built-in voltmeter, but it's the same size as my Big Daddy, which is to say, BIG, and not quite ergonomically ideal for holding in the hand while vaping. 3AA boxes are just about the perfect size for comfort. For many months, I've wondered who would tackle the problem of building in a voltmeter to a 3AA box dual-14500 VV. The VMU Innovate did this last year, but it was pricey ($90), usually unavailable, and I didn't like the button placement.
Now both Ken and Madvapes have come out with metered units similar to the VMU. Ken's are pricier, but he's a magician with cramming electronics into micro-sized spaces. Also, Ken puts his firing switches on the side of the box near the top. With both Ken's and Madvapes' VV boxes, I'm not thrilled with the tiny firing buttons. I've corrected that on all my Madvapes VV boxes by taking round "rubber feet" (1/8" thick and about the same diameter as a horn button), then drilling/routing a small hole halfway through one side and pressure-fitting them onto the switch buttons with a little dab of superglue for extra hold. That has worked very nicely
My last gripe/wish (mentioned above) concerns button placement. The VMU and the new Madvapes metered box use the center battery slot of the 3AA box for the electronics. That's fine---I like center placement best, but the voltmeter is on top, with the firing button below (in the bottom half of the front face). When you hold the box in your hand to vape, resting the box face up on your fingers, your thumb naturally falls near the top of the box. Having to move your thumb down to the bottom half of the box to fire is not only awkward, but tiresome.
That might be a deal-breaker for me. Lack of ergonomic comfort is one reason I don't own a Precise, GG, or other bottom-firing tube mod. Similarly, the top-firing mechanical button is one reason I don't own a REO Grand or Mini (although I do have two MaxiRoughStacks with top-firing switches). For box mods, whichever face the switch is on (front or side), I want the switch high up on the box, closer to the connector.
One thing I particularly like about Shan's Big Splash (and Red Sky wooden feeder mods, although I don't own one) is that the voltmeter is installed on the bottom of the box, both out of the way and normally out of sight. I understand that this placement is not possible on a 3AA box, however.
I'll probably end up getting one of the new Madvapes metered VV boxes, because I really like the Fairchild linear LDO regulator over the more efficient switching regulators. The linears hit like freight trains and work beautifully with any carto you want to throw at them, and I've never had a problem with excess heat.
I'm still resistant to the fancier VV tube mods that build in 2.5-or-less amp-limiting for "safety"---Darwin, ProVari, LavaTube, etc. But then, I much prefer step-down regulators to boosters.
