The mobility they afford easily makes up for any negative effects. I couldn't imagine working from a fixed computer. I even tried putting my laptop on a stand and using an external keyboard—it lasted a few days before I just got so annoyed by the fixed position. I sit facing different directions at my circle bar table, shifting my position multiple times throughout the day, so having a laptop that I can simply adjust as I adjust makes a lot more sense for me.
Wireless keyboard and mouse combined with putting the screen at eye level can solve these things. They give a range of motion and posture not available with the laptop itself.
Then again, I'm sitting on a computer with a wireless keyboard and mouse, in my living room chair, for many of the same reasons.
That's still not good enough because you will either have chipmunk arms (i.e. hands at chin level) or will have to bend forward to look at the screen.
There is a good selection of tenkeyless keyboards available that will fit in your laptop bag (get one with a microusb port rather than a fixed cable, as strain relief for a fixed-cable that's getting shoved in a bag is challenging).
Then you just elevate your laptop (stack it on books, bags, whatever you have handy; I keep a few textbooks on my desk at home for this) and put the keyboard on your lap if sitting, or bar if standing. I wouldn't call it perfect, but it's mobile, affordable, and way better than a laptop alone IMO.
>Get a proper laptop with fullsize keys and a large enough screen to work on.
No laptop in existence has a keyboard big enough for me. The smallest external keyboards I've used are probably larger than the largest laptop keyboards.
It's not about the size of the keys. It's about the location with respect to your shoulders. Having to angle your arms inwards is not a good idea.
Same for screen. If you're looking downwards, it's bad for your neck. Which is why I always use an external monitor.