This, from Home-Barista.com
“I've been reviewing a beta version of the machine for the last three months. The claims are mostly correct:
This is a very basic, small boiler, HX, vibe pump E61 box with specs mostly identical to the base Mara. What's different are the controls. There is a PID in the steam boiler which switches between two set points, one at around 2 bar, one at 1 bar. The setpoint chosen depends on the the temperature of the water returning from the thermosyphon into the boiler. This approximates the group temperature, and since this is a massive E61 group, it is also close to the same as the shot temperature, whether the boiler is at 2 bar, 1 bar, or somewhere in between.
The result is that you can make a no flush shot that goes as long as you like without worrying about temperature. But you aren't going to get a whole lot of precision either, roughly 90 to 92 at the low setting, 94 to 96 at the high, and 92 to 94 for the middle setting. This is about the same as you can get with Eric's group head thermometer and a flushing regime. Personally, I much preferred using this control to having to do it myself. But I've been spoiled with the Strega and Bianca, which are no fuss machines when it comes to managing temperature.
The three position switch is an honest control, since the nature of group makes anything more precise than about a 2C range on shot temperature impossible. For instance, on dual boiler E61s, the precise adjustablilty of the brew boiler is to some extent an illusion, since the shot temperature will also vary up or down in a two degree envelope or so. A three position switch would work just as well on an E61 DB.
On a historical note: Over the last fifty years, many companies have patented thermosyphon based active controls; and none, as far as I know, have made it into production. They've all been too finicky. Us hobbyists also have not come up with anything stable. What Lelit is doing, switching the boiler between a low and high setting based on the thermosyphon return, may sound really simple, but that is very good engineering in my book, a simple, stable solution to a fairly tricky controls problem.
In addition, Lelit has tweaked the group jet and and expansion valves so that you can use very fine grinds on this machine without choking it. It isn't quite as versatile as having a needle valve kit installed, but it does get close. Note: I have not used the regular Mara, so I don't know if that has the same fine grind tweaks. I am instead comparing it to older E61 boxes I've used.
Steaming is trippy, since you get close to commercial speed performance when the steam is up at 2 bar; and rockaby-baby-HX performance when it's down at 1 bar. There's also an initial warm up accelerator in the controls (similar to the Bianca), so if you catch it just right after start up, you'll see the steam up at 2.75 bar (!), and get a real rush on your cappa. (or a near heart attack the first time you see it, when you expect to get blown across room -- I'm sure the updated manual will clearly note this tweak)
I don't know what the price premium is on this version of the HX, but in terms of stability and no fuss, it gets you to about the same place as a double boiler E61, in a fairly compact, counter space friendly package.
I enjoyed using it. But people should note, this is not a "high tech" machine; it is a basic espresso machine that has been polished so it works like a simple tool, making no fuss shots. It's not a machine for people who want a lot of precise adjustments, or a lot of during-the-shot control.”