I've had a chance to look through a new-to-me pair of B5 18's that I bought from a member here. I've never looked through the SLC 15's so I can't comment on how they might compare to those. However, I did recently own a pair of Cabela's Euro HD (Meopta Meostar) 15's, which I returned to Cabela's. I did compare both of these to my Kowa 553 spotter as some sort of a standard.
In a nutshell, the B5 18's are an exceptionally powerful tool. Being a pair of binoculars, the effect of the high magnification is remarkable. It leads me to think of these as a super compact version of the Swaro BTX. On paper they're almost twice the magnification as a 10x binocular and they really do feel like it when I look through them. The image is sharp almost all the way to the edge, better than my Nikon Monarch Hg's, I'd say 90-95% of the way to the edge, this is similar to the Meopta's. The depth of focus, which I was worried about, is actually quite forgiving in my opinion. The focus adjustment is a bit quick but it turns very smooth and has just enough stiffness to not easily overrun the sweet spot. The interpupillary distance is great as others have attested to. The limited exit pupil doesn't seem to be a problem to me. It looks plenty bright enough. Testing it against my Kowa with a similar size objective, it really highlighted how dark the Kowa gets passed 25-30x. Another way to think of it, if we crunch the numbers against the BTX, these have greater objective glass area per magnification, so it really shouldn’t be an issue. The only negative I have found with it is my sample definitely has some chromatic aberration issues with the sharp white edges. It's not bad, similar to the amount of my Nikon HG's have, but noticeable. I may be a bit harsh on that characteristic as that was one characteristic that the Meopta's were stellar at. I looked real hard through the Meopta's to find any and I couldn't. Again, the Maven's CA control is as good as the Monarch HG's which are highly regarded.
To me, and for my purpose, I find a better value in the additional 3x magnification of the Maven's than the better chromatic aberration control of the Meopta's.
The little Kowa sent the Meopta 15's back to Cabela's as their magnification couldn't compete with the Kowa but I think there's very little that the Maven's can't see that the Kowa does. So with the pleasant two-eye viewing experience and far greater field of view, I think these will probably end up sending the Kowa down the road.