So I've gotten my HHKB Pro 2 since after all this time, I really wanted to try it. What I'm about to say might rustle a few jimmies, but alas, in case anyone is trying to decide whether or not to try it, here are some thoughts.
The HHKB feels harsher than the Realforce 87U 45g. I'd say that the key weighting feels a bit heavier than the 45g in the Realforce. The sound is a lot harsher since the bottom-out sound is louder, the upstroke has a sharper but lower-pitch sound, and there is quite a noticeable amount of grittiness to the keys (some more than others).
I'm thinking of trying to figure out some way to sound deaden the case and maybe try lubing the stems because right now, it feels like a cheap version of the 87U. The Enter key makes a thud, some keys are quite a bit louder than others, the spacebar makes a bit of a hissing/gritty sound. The outer keys (ASD-L;') sound pretty good (fairly quiet, high pitch 'click' on upstroke) while the central (FGH) keys sound very harsh (hollow thock, loud 'clack' on upstroke). It makes for a pretty uneven typing sound. By comparison, the keys are far more consistent with their sounds on the Realforce boards -- they still vary a bit, naturally, but it sounds like one keyboard.
The layout isn't bad, though it would make a lot more sense to have the backspace/delete keys better sorted (or at least more options using the dip switches). Using the function key for arrows and navigation isn't all too bad, really, though if the function key itself were lighter I think that would feel better for my pinky (it doesn't like heavy keys much).
The build quality is generally pretty good, though the top case is slightly overhanging the bottom case on either side by quite a bit, which feels funny when you pick it up or move it from its sides.
After typing on it for a bit, I can kind of look past some of its qualities, but the moment I type on my Realforce it feels much smoother and more refined, as well as sounding better. The typing angle is noticeably steep. It isn't too bad when I'm sitting, but on my standing desk you can really tell. I suppose this depends entirely on your typing setup.
I really wanted to love the HHKB (at nearly a whopping $400 Canadian by the time it gets here), but right now I'm just not so sure. I do enjoy typing on it still, but it's hard to like it enough to have it worth this much money.
I do like how light it is and having the USB ports on the back is certainly handy at times. I'll probably report back after using it for a few weeks. Right now, between the two, I'd say the Realforce 87U is the better of the two, especially for use around people who might not appreciate the various thocks and clacks from the HHKB. I also really don't think the HHKB is worth the amount I spent on it, though much of that is due to the Canadian dollar and import charges right now.
Here you can see the typing angle of the HHKB vs the 87U (and some other boards):
And while I have you here, I might as well show you my KUL ES-87 and QFR with some nice PBT keycaps.
They look better in person as the lighting and white balance is off but you get the general idea.
EDIT
Update (copied from later post):
Although I still maintain all my original critiques of the HHKB, I really do enjoy using it. It's fun to type on and the layout really isn't too bad. I would change a few of the secondary key positions -- they make sense logically where they are, but they are less practical. For example, I would move the 'PrintScreen' from the 'i' to the ']' key just so that it's easier to reach.
I think I'm going to add some sound deadening to the case to reduce the hollowness and hopefully reduce the gritty sounds. I might also lubricate the stems and see if that makes a difference.
I am definitely keeping this keyboard though and I don't regret buying it, even though it cost an unreasonably high amount to get it here in Canada.
One thing is for sure: it has character... and whether or not it's objectively great, it has that second kind of cool that just makes you want to keep hacking away on it.