The principle of a vacuum brewer was to heat water in a lower vessel until expansion forced the contents through a narrow tube into an upper vessel containing ground coffee. When the lower vessel was empty and sufficient brewing time had elapsed, the heat was removed and the resulting vacuum would draw the brewed coffee back through a strainer into the lower chamber, from which it could be decanted. The Bauhaus interpretation of this device can be seen in Gerhard Marcks' Sintrax coffee maker of 1925.
Moka pots, also known as stove top espresso makers, are similar to espresso machines in that they brew under pressure and the resulting brew shares some similarities, but in other respects differ. As such, their characterization as "espresso" machines is at times contentious, but due to their use of pressure and steam for brewing, comparable to all espresso prior to the 1948 Gaggia, they are accepted within broader uses of the term, but distinguished from standard modern espresso machines.

Some home pump espresso machines use a single chamber both to heat water to brewing temperature and to boil water for steaming milk. However, they can perform only one operation at a time, requiring a warm up period between the execution of espresso pull and the milk frothing process. Since the temperature for brewing is less than the temperature for creating steam the machine requires time to make the transition from one mode to the other. Moreover, after the brewing process, a single boiler will expel (usually minor) quantities of water through the steam wand that were left over from brewing, which can cause the steam heated milk to then have a slightly watered down taste. To avoid this, the leftover water needs to be collected from the steam wand before steaming of the milk should begin. SB/DUs are generally found within the lower tiers of enthusiast home models, with steam wands being a simple and valued addition.
"A rare example of the meeting of form and function. This machine is both beautiful to look at and makes wonderful delicious espresso and cappuccino. I was hesitant to spend this much on a "coffee maker", but took into consideration what it costs to get a decent cappuccino from a cafe or Starbucks and finally gave in. Boy am I glad I did. All it takes to get me out of bed in the morning is the happy thought of pulling yet another delicious shot from this wonderful machine."

The simplicity starts with its design: a single button with a scrolling dial underneath an LED interface. That button is the only one on the entire machine. With it, you set the time, set the water temperature, set how many cups you want brewed, and when you want the brewing to start. It takes a second to get the hang of it, but we were impressed with how intuitive it is — a stark contrast to a machine like the Moccamaster KBT 10-Cup Coffee Brewer, which had so many extra pieces, it required constant consultation of the instruction manual.
“I like the Technivorm Moccamaster because, from a scientific standpoint, it creates the proper water temperature (and temperature consistency) for good extraction of flavor from the beans. That’s the problem with most cheap automatics — they’re inconsistent about temperature. It also has a shower-head design for good water dispersion and saturation of the grounds. It consistently tastes almost (almost, I stress) as good as a manual drip.” — Andrew Chou, engineer, General Motors
As for the seller: when the unit was originally delivered the steam wand wasn't performing well. After following the typical trouble-shooting tips and conferring with the seller, we found the unit was simply unable to produce enough pressure to steam or properly brew. Within a week the seller had replaced the unit, and I'm happy to report it works perfectly. No matter the production value there is always a possibility of a defect here or there. The seller standing by the product and immediately replacing it to our satisfaction really sealed the deal for us. I highly recommend both this product and the seller from whom we purchased it."
Why it's great: A true espresso drinker knows that when it comes to espresso, there are a few things that can't be overlooked when it comes to a quality cup: freshness and a good grinding method. The burr grinder is a known Barista-favorite, as it maximizes the surface area of the grinds resulting in optimal flavor. The BES870 even allows you to adjust the grind and portion size, so you can go from fine to course depending on your desired flavor. 

Our brew-performance tests measure the brew temperature and contact time (how long water stays within a sweet spot of 195° to 205° F for brewing). We measure concentration using a refractometer, a device that measures the amount of coffee dissolved in each brew. Our convenience tests look at how easy it is to set timers, fill the reservoir, clean the machine, and more. And for the first time, we’re incorporating predicted reliability and owner satisfaction ratings into the new Overall Score for each model. We determine these ratings for each drip coffee maker brand using survey data collected from thousands of CR members.