Well, for a 9.7" iPad, a "full size" keyboard is larger than the size of the iPad.
The keyboard case (which is a small keyboard that's harder to type on) that I have essentially doubles the weight of the iPad, which makes it much less compelling.
So yes, I actually think the portability will be a big deal. Even if it's just iPad + Smart Cover + TextBlade, being able to take that with me is going to make a huge difference. Quite possibly the difference between not bothering and having it when I need it.
Just the other day I took my iPad and was doing work on it and wished I'd brought my keyboard. Of course, if I had to lug the keyboard along I probably would have given up and just brought my laptop. So a TextBlade is that bump in portability that allows for the iPad to become the device of choice. I imagine I'd just stick a TextBlade in a pocket in my bag and it would be there for whatever device I happen to be using.
I think the portability really comes down to three areas:
1) Size. Both transport and usage.
3) Key feel
As for size, the TextBlade pretty clearly wins in transport and its noticeably smaller in usage as well.
As for weight, the thing is apparently quite light. That's a big win for me.
And all reports indicate key feel that's really excellent. Not a compromise to achieve 1) and 2), but actually arguably better than other keyboards due to the spacing, magnets, travel, etc.
I think this is huge. Generally you'd expect to sacrifice one of the above to get the others, but having a product that can win in all three areas is what makes it truly revolutionary instead of a cute gimmick.