If you are a flaming anti-vintage-stove fanatic (I did NOT plan that pun. Wish I had), I have no idea how you ended up here, but since you are, let me guess on the reasons for your viewpoint. I'll make this as quick and painless as possible.
Your issues with vintage stoves probably center around three things: it's unsafe, it's far less efficient, the oven is too small.
I cover safety elsewhere, as well as the insanity of granting "Energy Star" ratings to ranges that in 10 years will end up as metallic chips being shipped back to China to be re-formed into brand new "Energy Star" appliances, then shipped back here.
For now I'd just like to start by backing up a bit up and getting one thing out of the way: the overall negative connotation surrounding "vintage". As in "Ma! Ya got a vintage stove! I'm gonna get that clunker outta here and get ya a modern stove." Vintage meaning "old" and Old = Bad?
With parachutes, medicine, diapers, a gallon of milk, I'm sure we all agree: old is bad. What about wine, cheese, Mozart, a '66 Mustang GT, the Grand Canyon? Picasso? You would never discard any one of them out of hand, just because they are old. Dear old Ma might be a pain, but where would you get Ma's chocolate chip cookies from, without Ma?
So we're agreed? Old can be good? Great. Let's move on to efficiency.
It's not a myth, it's simple math: the energy efficiency of a Chambers compared to other gas stoves is off the charts, easily understood by pointing out a few numbers.
First and foremost: R value, the capacity of an insulating material to resist heat flow. We are talking massive R value here from the mineral wool insulation - the same stuff used to insulate kilns - that is densely packed into the jacket surrounding the oven (and ThermoWell). No other stove has this.
Chambers stove insulation
Even when a Chambers oven is used conventionally - just turning the gas on and letting an item cook - very little gas is needed because the densely packed mineral wool prevents the heat from passing through the oven walls, far better than a thin layer of fiberglass used in other stoves.
Utilizing the Chambers Retained Heat cooking feature ratchets up the thermal efficiency to an even greater degree (No, really, that just slipped out. No pun was ever intended). Normal ovens have a "passive" inlet and exhaust system, basically holes in the floor and sides, which creates the air flow necessary for the process of combustion. This flow of cool air into conventional ovens occurs all the time: it cannot be stopped. Even when the gas is turned off, as long as the air in the oven is warmer than the air outside of the oven, the flow continues, rapidly cooling the oven. A Chambers, however, controls the airflow via an "active" airflow system. When turned on, the oven's "on/off" lever opens inlet and exhaust flaps. When turned to "off", the flaps close. Cool air can't enter, hot cannot escape. This sealed, highly insulated thermos is what makes retained heat cooking possible. Chambers marketing materials claims that CWTGTO uses about 1/6th of the gas of a conventional oven.
The third gas saving measure of a Chambers oven might be the least obvious, but it is quite significant. It's actually shared by most stoves made before the mid 1960's: the small size of the oven. A Chambers oven measures 18" deep, 18" wide, and 12" high. The volume works out to only 2 1/4 cubic feet, compared to modern 30" ranges, with 4.2 to 5.8 cu. ft. So with less than half the volume of the majority of today's stoves, it's no wonder why this is the foremost "deal killer" objection I hear about keeping or purchasing a Chambers.
But think about it. Is the "small" oven really a problem? Or is it a misconception?
Consider all the times your oven has been used in the past year. Of them, how often has it been heated up to warm, bake or roast a small item? Think about how much gas and time it takes to pre-heat that large oven, how much gas it takes to keep that huge oven hot in order to cook a small item? How few times have you actually used it's total capacity? How much space do two or three cookie sheets take? How about a pizza? A large turkey roaster? The "small" Chambers oven can handle them all. You see where I'm going: the "small" Chambers oven requires half the gas, and can easily handle 90% of items put into a "normal" oven in the course of a year. So if it covers most of our needs, why call it "small"? If a "normal" sized oven covers so few of our needs, why call it "normal"?
How about we change "small" and "normal" to "optimal capacity" and "extra capacity" to get a better sense of what's going on.
A Chambers' "optimal" oven has enormous energy saving benefits over an "extra" capacity oven due to faster pre-heat and less gas volume required for pre-heat and for cook time. Add to that the Chambers' mineral wool insulation, active air flow controls, and the thermal mass of its cast-iron oven bottom, and you can see how a Chambers' oven makes total sense, not just for responsible stewardship of our environment, but for practical, convenient, everyday use.
When buying a car, we make very conscious decisions around optimal use, and purchase accordingly. Regarding size, sure, a full-sized van might handle any and all needs for however many people or things we might need to move from one place to another, but most people don't need that capacity every day, and/or are unwilling to pay for the extra fuel it consumes. Does it make sense to own and use something every day that uses so much fuel, if we only need it's capacity once in awhile? Why not look at stoves the same way?
For the times when extra capacity is needed, check out my post of 11/9/15.