I bought this Midori MD Paper Cotton letter pad from Jetpens a few weeks ago, and have been using it regularly ever since. I am quite impressed by the quality and feel of the paper, it has some tooth, but just enough to notice, not enough to be annoying when using a sharp nib.
It is very resistant to bleed through, and the color balance of the paper (somewhat off-white, but not quite ivory) shows off the brighter inks very well. The paper is thin, not quite Tomoe river thin, but still a thinner paper than you might expect given it’s wonderful performance.
The lines are more widely spaced than I would prefer, but they are grey which I like, and have good margin width, which makes the letter seem more substantial.
Which brings me to the size… This isn’t a standard size, it is about the height of an A5 paper, but has a width which is about the same as a B5 paper, so it is closer to a square than a tall rectangle. The size is pleasant, and I see why it was chosen, but it presents a problem: envelopes have to either be made to size (Which I have done), or the matching envelopes have to be purchased. (Which is very expensive), you can also use a regular long envelope and do a tri-fold, but I much much prefer a single fold, and so I have to use the matching envelopes despite their cost. I think that is an area that Midori can improve, the envelopes cost about $1 each!
The paper can take a light watercolor wash with no complaints, there is some ghosting and a bit of wrinkling, but no bleed-through and no sign of the paper weakening.
Overall; I really enjoy using this paper, and I will keep it on hand as long as Midori continues to produce it.