The real advantage I see from a uni-mount is if you want to remove/re-install with minimal zero change. Also I'd imagine that it's easier to keep tolerances, strait/round etc. with a one-peice so there's less stress on the scope body, where with individual rings the rings might be machined perfect but they are subject to the rail. You can also get built in elevation with uni-mounts so in some guns like an AI/TRG you can then eliminate one component (rail) and clamp directly to the action. My guess is they are more expensive because they need a larger chunk of stock, and there is more waste material. There are also quite a few good proven uni-mounts for $200 and under, Seekins, JP, badger, etc., so you don't have to drop $400+ on a Sphur.
The HUGE disadvantage I see to one piece mounts is you have way less flexibility in scope position. Especially with units like the Sphur where the rings are super wide. I have two of them with Razor Gen 2's and you basically have no give in moving the scope forward/rearward in the mount, maybe 1/8" tops. As a result you lose one of the ways you can adjust scope position. Individual rings are much more flexible in their position and the scope within them. That allows the shooter much more flexibility to get the right head position and the right LOP.
In decades past that wasn't a big deal because everyone was shooting what we now are realizing was too long of LOP. The old rule of thumb used to be put the butt in your elbow and the right LOP was where the tip of your finger was, now more are going to using a LOP that matches if your trigger finger is bent 90 degrees and that difference can easily be an inch. Now that many are shortening their LOP they are running out of room to move the scope far enough forward before they run out of action rail. My TRG is a great example, I had to put a spacer into my stock beyond what I wanted for my ideal LOP because I simply could not get enough eye relief with my Razor 2 even with the Sphur mount at its most forward position.
Also don't assume lower is better, I see a lot of guys with bad head/neck positions because they are trying to shoot the lowest rings possible, you want to be comfortable with the right head/shoulder position behind the gun that is repeatable and maintainable. If you are sacrificing body position to see through a scope that's too low, that's just as bad as too high. The same is true for bipods, everyone used to think lower is always better but we've learned that many shooters are doing better by going a bit higher which provides a better body position for them.
