I used my neighbor's Kobo HD while I was setting it up for him. I have a Kindle Voyage. The Voyage in it's cheap, very light case weighs less than the Kobo HD without a case. The Kobo is considerably larger.
While the newest H2O is smaller and lighter than his HD it's still closer to the size and weight of the HD than it is the Voyage.
The Voyage has a big size/weight advantage and to say otherwise is misleading.
The advantage of the Kobo is the larger screen, although that doesn't matter to me. I'd prefer a smaller screen but my neighbor does prefer the larger screen by a lot.
The Kobo has a number of software features the Voyage doesn't have but with sideloaded books most of them are fairly unreliable, not working as often as they do work.
The Voyage has a better screen although I'm sure the new H2O has much improved that. Still the Kobo HD screen is excellent even if the Voyage screen is a bit better.
As for the flush screen, I've been a big fan of that for a long time but lately I've been reading a lot on my Paperwhite and going to the Voyage while the Paperwhite is charging. I still prefer the size and weight of the Voyage but I'm starting to realize that I have to be a lot more careful where I put my fingers while reading. I accidentally turn pages more on the Voyage because of that flush screen. That doesn't happen enough to be a real problem but it happens enough to make me wary of it and draw my attention from my book. I still like the luxury of the flush screen but I'm starting to think it comes at too high a price.
I think the most important thing to realize when making an ereader decision is that these are all very fine points. These are all excellent devices. When you're choosing between perfection and magnificence it's pretty hard to get it wrong.
Big Bad Wolfe, please read that last paragraph again.
Barry