I have the Keys and recently added the Rytm.
You can use the Keys on the couch, but it’s hardly the most ergonomic solution. If you put it in your lap, even with a lap-desk, you have to do “Tyrannosaurus Rex arms” to play the keys and then your elbows are poking into the couch cushions.
If you put it on a tray table or a typical keyboard stand, it ends up too high because you are sunk into the couch cushions.
I’ve had the best results putting it on an ottoman that puts it at the right height for my hands and sitting on the edge of the couch, but even then I have to kind of lean over to counteract the natural tendency of the couch to suck you into a lazy slouch.
Simply not the best experience.
The Rytm, on the other hand, is totally a use-anywhere device (as long as you have somewhere to plug it in and headphones). On the couch, in bed, on a train/plane that has outlets…it’s very happy to travel. And chromatic mode means I can easily write a whole song on the Rytm, so I don’t mind leaving the Keys behind when I do go Elektronomadic.
I do love the Keys, and the features it adds. And Overbridge is not going to diminish that opinion, because individual outputs that require a computer-sized dongle to work are not the same as built-in 1/4-inch outputs.
If you think those features are worth having, I’d advise you to get it and just use something else on the couch - the XioSynth is pretty cheap, as are apps for the iPad if you already have an iPad, or one of the Pocket Operators, or an old Yamaha QY-70, or a Volca.
If you think you can live without the AK’s extras, then get the A4 and join the Elektronomad caravan.