I think the real advantage will be using this set up varying from 17x, 25x and 30x as different conditions are encountered, and, if you see something at distance, that needs a closer look the ability to go to 40x almost instantly without switching optics and taking an eye off the prize (this has hosed me so many times)
The other big one for me
and hopefully it works as sweet as I think it will-
Let’s say I’m glassing a hillside or a basin, in this basin is a place I have known deer to both feed and bed… open easy to glass country with broken cover for deer to bed….. typically I would cover it with binos, then I would use a spotter in bedding areas and thick stuff, looking very thoroughly and at higher magnification, say 30x, looking for bits and pieces of deer, and any movement.
To be effective and not miss deer, I am also keeping a close eye on the rest of the easier to glass country at lower magnification to cover it the most amount of times possible.
To do it all justice and maximize coverage, id be switching back and forth, between 15’s and spotting scope, an easy 40-50 times a glassing session. Wasting time every time I switch.
With this set up, one twist of the wrists and I’m going back and forth on magnification, eyes never leaving glass, looking close where I need to and getting maximum field of view where I don’t.
I think this set up will make you more effective, especially in the golden hours of deer moving. I’ll know soon as I get more time behind it.