They're for different uses. I'd say the full size ones are better if you want a bike that would fold for storage, rather than for transport.
I've had three 26" folders before getting the Brompton and have to say that none were as useful for me.
The 26" one is great if you want a 'normal' bike that just about gets around the rules for folding bikes on trains.
My last one had front suspension, but I used to lock it out as it was way too springy and just sapped any energy you put in.
I would have ended up putting rigid forks on it if the frame hadn't snapped.
As mentioned above, most of the parts are available already and are produced very cheaply to satisfy the global demand for cheap BSOs. That's Bike Shaped Objects - things which look like bikes, but are in fact rubbish.
Whereas there doesn't seem to be much that's standard about a Brompton, for instance.
That's a good thing and a bad thing in many ways. When parts are standard, but cheap, they're easy to upgrade. If they're one offs, and you don't like them, you have no choice but to work with it.
At £1,080, my Brompton ended up about £300 more than my Dahon Matrix, but I'm hoping that in will last a lot longer than the four years my Dahon managed before it was junk.