9 month critical review:
MOST SOLID WIRELESS MECHANICAL KEYBOARD OUT THERE!
Awesome keyboard! My first and only mechanical keyboard, so I can't really tell for the mechanical keyboard part, but I believe this is the same quality as the other Majestouch 2 keyboards, so you can read about these elsewhere. It does however add some build in media keys through a function layer, and detachable cable, compared to the basic wired version.
About the connectivity part: the Bluetooth connectivity is perfect, almost! Connecting is very easy under Windows. Linux will require the latest drivers to be running, I personally had to upgrade and fix some stuff, but it now works as well as in Windows. I didn't encounter any problem with my Android devices either, old or recent.
Very rarely you may encounter some bugs like it keeps sending the same character over and over again even though the key is not pressed, until you eventually turn it off and on again, but it's so rare that it doesn't spoil the user experience IMO. (once in two weeks, or in a month? I can't tell.) This will also happen with the wired connection as well, in which case you'll have to plug it off and on again. But absolutely no problem with typing at my speed (90 wpm) and not a single missed keystroke: you simply won't tell the difference between this and a wired keyboard. Apparently this is not the case with all wireless mech boards available, hence the title.
The multi-device mode is flawless and very convenient. It allows me to switch OS in my dual-boot system without having to configure anything, have my android TV box saved as well, and an extra fourth slot for occasionally my tablet or my phone. The corded connections lets me use it with older PC's that don't have a Bluetooth module, or under Linux when it is having a bad day. It fulfills all my needs, and more!
One reproach I could make is that switching between devices isn't as sharp as in, say a Logitech multi-device product. You'll have to wait a few seconds with the blinking lights before it works. Again, strangely, this is also true for the wired connection: when using the keyboard with a Desktop PC, and powering it on for instance, the keyboard will not connect automatically, and you have to press one key and wait a few seconds with the lights blinking for the USB connection to be established. This takes a little off from the premium, and I hope that this will be improved in further iterations, make's it look less sharp, but still very solid. I know it's possible to improve, since I see this for instance at Logitech's, but they don't have a multi-device mechanical keyboard, yet.
Finally the battery-life: simply, I can't tell, since I didn't have to change the batteries once since I bought it last November (9 month ago) ! I must say I have a moderate use, so that's like mostly 4 hours per day, sometimes more, like when I have to write a paper work, sometimes letting it rest for a week, and occasionally switching with the wired connection. Still an amazing performance compared to other wireless keyboards that don't offer this multi-device feature (though they have back-lighting, but I am not into this) and have their battery-lives counted in weeks only.
Portability: upon using it I realized that the tenkeyless form-factor is not the best choice for portability. At nearly 1kg (2.2 pounds), you might prefer a wired 60% keyboard to this one (or the minila air from filco, which is moreless the same product in term of connectivity and battery life (mind, there is no usb), but I don't approve it's unusual layout). It does fit in the bag, but I wouldn't take it back and forth between two places on a daily, or weekly basis. It's best laying on you desk, and moved around in the house.
The only thing I could wish to make it perfect is a programmable feature, but I guess you just can't have everything at once in life!
Conclusion: I'll rate it 4 stars because of the little improvements that can be made (and also the high price), but that's more like 4.5 stars and I highly recommend this product as a first choice to anyone who is looking for a wireless mechanical keyboard solution.
PS: this review was happily typed from my couch on my majestouch convertible via bluetooth!