A few thoughts after having used it as my standard journal for a few weeks:
I don’t actually use it while travelling. Not that I travel much anyway but I can’t see that it would be all that preferable when doing so – it is durable yes, but the flexible cover would make it awkward to write in when there isn’t a convenient flat surface, which is more common when travelling.
The plain paper refills are my favourite.
The extra-thin paper does take ink very well, but I had two problems with it. Firstly, ink looks a little odd on it; it seems to dry with a little edge around the letters rather than shading as it does with normal paper. Secondly and more importantly ink is much more prone to smearing, even after days of drying. This may be unavoidable if it isn’t going to bleed, but I found it annoying enough to stop using the refill after ten pages or so.
On the subject of annoyances, if anything is likely to make me stop using the thing, the way that the pages don’t lie flat is likely to be it. Particularly as you approach or leave the middle of the book and the cord starts to force the edges of one side up even more. Having a secondary refill in there doesn’t help either. This is a basic issue with the design and I doubt there’s any getting around it – I will just have to decide whether it is annoying enough to overcome all of the plus points.