I hate to say it, but you know it's true: grapes, sour...
While I gladly accept that the ProVari is not the absolute single best device for anybody ever, this is getting dumb. ProVari is an excellent PV, bordering on perfect. The build quality, the performance, reliability and ease of use are matched by few others, and as far as price - it is cheaper than a lot of other high end APVs. It sits on the border between mass produced and small series so there's arguments to be made about the price point back and forth but who cares: the ownership experience is fantastic and that's all that matters.
See - there are other good VV devices, and each has something specific to offer. The mix of features of the ProVari is not found elsewhere. Hence, you have a choice, and a lot of people chose the ProVari. True enough, some just get it because it "sounds" like it's the only game in town which is probably not correct. But if you know what it is, and if you want great performance and a luxury feel - well, go for it and - yes - don't waste money "dipping your toes" with other devices.
However, I'll try to look at some alternatives as objectively as I can:
Going down the ladder - the Darwin has better performance and offers the more attractive concept of variable power instead of voltage. It stands in a class of its own, no debate about it. That's cool if you can get over the form factor and the impossibility of actually buying one. Other disadvantage - built in battery that you can't swap out.
The Buzz / Infinity are good and stable and reliable and powerful, but they use stacked batteries (which is not a huge deal given all their protection features). The concept is that instead of boosting one battery to the required voltage, it trims down the double voltage of two batteries linked in series. That has the advantage of a longer battery life, and the disadvantage of you having to always charge batteries in sets and make sure they have the same charge at all times. And they look... differently. I find them very ugly, some find them beautiful - the point is looks matter in some way.
Mechanical mod + the Kick - the greatest advantage is that you get an APV that will function on its own indefinitely and will be variable power for as long as the Kick kicks. The other advantage is that you get to choose whatever looks you want. The downside - limited power with the Kick and perhaps price: if you go all out on a fantastic mod, then add the price of the Kick you may end up spending more than on a ProVari. Another choice is Silver Bullet + Kick which is definitely attractive; although not mechanical, the Silver Bullet has an unstained track record of reliability and longevity, so there.
VV Reo / Woodvil - fine looking, awesome performing bottom feeder APVs with the circuitry found in Buzz / Infinity. If you already use and like bottom feeders then it's a no brainer. If not - it's a little tricky to switch vaping paradigms completely only for the variable voltage. They are also difficult to get a hold of.
VMax - unless you have some anti-China bias and you can get over the shameless way in which they copied ProVari's looks and Buzz's circuitry in their device it's probably an attractive choice. Reviewers pointed out that the supplied voltage doesn't match the displayed one, which is not a problem once you're aware of it. It is also a stacked battery design. The other annoyance is that it resets when you swap batteries, and it resets to a high voltage so you have to be on your toes or you might burn your cartos.
LavaTube (by any other name) - it's sort of cheap, and it feels and looks that way even in the new shiny stainless steel version. In any event, it seems the newest version performs well compared to the old, and maybe there are fewer reports of flimsiness and unreliability. It's not a bad device, overall, but don't expect the same feeling of luxury vaping you'll get from higher end devices.
VVPV - another Buzz/Inifinity derivation, this time a top feeder. If you can ignore the Borgish look with the plastic tube wrapped around the atomizer, it's an interesting proposition as well. Looking at the classifieds, it seems there are major issues with build quality, though.
SVR / Evo - not really variable voltage (it has like three settings). I don't know much about this one - it looks cool enough, but there have been some QC concerns in the past. It has some nice features, but I for one like being able to tweak the voltage in small increments rather than having a few presents. Remember that power depends on voltage squared, so small changes in voltage make for large effects.
Did I forget anything important?
Sure - you can get similar results with cheaper devices. Sure - some people don't feel they need a ProVari or even variable or regulated voltage. It's a world of personal preferences.
There is a difference between signaling that some people sometimes push ProVari regardless of the OP's question, intentions, desires or budget, and there's a whole different thing to imply that this massively successful PV is all hype.
Anyhow, regarding size - the ProVari standard, with 18650 extension cap is about as long as an iPhone and slimmer than a quarter - hope it helps you gauge it.