Time for an update.
Finally got these EPs out under some dark skies last night after a few weeks of light-polluted backyard observing. Scope: f6 200mm Dob.
13mm Stratus and Nagler
As some of you would know I already sold my 13mm Nagler. So that should tell you what I think of the 13mm Stratus. Very comfortable, easy viewing with very little to complain about. Looking for the 5th & 6th stars in the Trapezium in marginal conditions, it seemed at least as capable as the Nagler as far as resolving detail goes. The Stratus has some light scatter off the edges of the lenses that is not pretty when a bright object is on the edge. But this is essentially a non-issue, unless you like looking at planets with them sitting half in half out of the FOV. Unlike the Nagler, there are occasional internal reflections when looking at bright objects but nothing devastating. This is true for all the Stratus EPs not just the 13mm.
Now that it's sold, I can say that I found the 13mm T6 Nagler to be a bit of "try-hard" eyepiece. The characteristics of the optics seem to change quite abruptly from 50-60% of the FOV outwards. I don't know what it is exactly, but I just got the feeling that it is a weird, unnatural(?) design that is trying to push very agressively the limits of what is possible within the design parameters. I still love the eyepiece and nothing beats the ultra-wide field, but at the price I felt it's not good enough. There I said it!
Had the Nagler been 2/3 the price it would have been a keeper instead of the Stratus at little over 1/3 the price of the Nagler.
General comments on performance
Edge performance is very good with all the Stratus EPs. Best way to describe it is by comparison with the Panoptic. Looking at the flaws at any point in the FOV of the Panoptic (abberations like false colour, "softening" or little bit of seagulling), they seem to be about nearly twice as bad at an equivalent point in the FOV of the Stratus. Now, this is still very good, because twice a small aberration is stil a small aberration; and in the centre: twice nothing is still nothing.
The most obvious flaw to my eyes is the false colour from 75% outwards on bright objects like planets and the brightest stars. Stars have a bit of a blueish tail - like I tried to explain above -, similar to the Panoptic, but the tail is about twice as long in the Stratus. The false colour is not much of an issue though with most DSOs, and planets can be placed closer to the centre of the FOV.
Power to the People: 5 & 8mm Stratus
I found the shorter focal length (5 & 8mm) Stratus EPs very nice for higher magnifications without the very short eye relief of typical short FL EPs. I tried them alongside my HD orthos on the Moon, Venus, Mars, Saturn, globs, and a galaxy or two. While the orthos have superior image quality (esp. wrt. contrast), I can see the comfort factor of the long eye relief winning in the long run, with the orthos being kept for the occasional closer look. With the Dob, the wider field is nice too, because you can turn your back on the scope a little longer and still have the object in view. Also even if it does go out of view, the wide field makes it much easier to search for it by panning around.
Colour "temperature"
Looking at Mars and Saturn, colour seems a bit on the warm side in these EPs (perhaps also with a very slight hint of yellowish tinge on the Moon), compared with HD orthos. I found surface features on Mars easier to make out in the orthos, and I believe this is at least in part due to their more neutral colour transmission.
21mm Stratus & 19mm Panoptic
Finally, a few words about the 19mm Panoptic - 21mm Stratus comparison. I still haven't decided on the fate of my 19mm Panoptic. It is my best, most comfortable EP, but the 21mm Stratus is not far behind. The biggest issue for me is eye relief. For me, the Pan is perfect, while the Strat has way too much ER and it can get a little difficult to keep my eye centred on the huge lens when panning around (no pun intended) with the Dob. Kind of like the Radian I tried at Snake Valley. (The 21mm seems to have even more ER than the other Stratus EPs.) Maybe an extended eyecup would help. In other more subtle ways the Strat is just a little behind the Pan in performance, but it's pretty darn close. So is that little bit of extra performance worth over $200 or 2.3x the price? I know that only I can answer that... It is a really difficult decision because I can see myself regretting either which way I go. It's a lot of money, and I want to get into binoviewing some time in the future, and then expensive EPs will become twice as expensive.