My brother has a recent one (purchased 2018) which I have used on several occasions for long-distance raptor spotting.
In the hand - build quality feels superb, giving the impression of great integrity and reliability. Controls (focus, diopter, hinge, eyecups) are smooth, firm and positive, the usual Swarovski quality. I actually think I like the "dinosaur skin" rubber armouring a little better than that used on the ELs.
There's no getting away from the fact that this is a very big binocular by normal standards though. It is a big handful to hold, its weight, although not a problem when supported (elbows propped up etc) makes itself felt if you have to point it upwards for any length of time.
To look through - Sweet spot is very large, I would agree with the 80% figure you noted. 5.6mm exit pupil makes for very easy eye placement. Brightness is superb, one of the brightest binoculars I've ever looked through and almost too bright when searching against the background of bright white summer clouds. Resolution would seem to be excellent. Although the real measure of its capability in this area (like most large 10x binoculars) can only really be seen when tripod-mounted or otherwise stabillized. Most of my use is hand-held but supported (elbows resting on a shelf or other structure). When used this way it is still possible to discern considerable detail at long distance and birds of interest can be followed even after they have diminished into miniscule black flickering dots. Performance against glare and similar difficult conditions is good, better than the 8.5x42.
The image has the washed clean look that is probably the result of high transmission, sharpness and excellent CA control. Colour rendition matches what I see with my eyes very accurately, warm colours don't stand out as much as eg. with the Noctivid.
Misc fittings - Objective covers are not as refined as the ELs, but do the job OK. The strap itself is very good, providing plenty of support for this heavy binocular, but we have had the webbing connections occasionally twist up. A heavier grade material would help.
Some comparisons:
with the 8x56 SLC - I agree, and have noted before, that the 8x56's image has a kind of outstanding beauty to it that is really quite remarkable and which the 10x56, excellent though it is, does not quite duplicate. The 8x56 image, I agree, is more beautiful to look at. But the 10x magnification is (to me anyway) much more useful in a x56 binocular than 8x.
with the 10x54 HT - this was only for a period of 15 minutes or so at Birdfair a couple years back. Perceived brightness is similar and the HT is lighter and handles better. Optically the HT is a very strong performer. But both my brother and myself preferred the view through the 10x56 SLC. If I remember correctly, we felt the sweet spot was somewhat larger and the view moer effortless. SLC also gave the impression of superior build quality.
with the 10x50 WX - field of view is significantly smaller, obviously, so you see quite a bit less of what is in front of you. But what you see within its sweet spot compares very well. The SLC seems slightly brighter.
I have the use of my brother's example and if you have any details you would like to check, I can get hold of it and do what I can to assist.
Regards,
patudo