The most accurate balancer is possible to 'build' your self.
A bit cumbersome explanation, but bear with me...
Go to your hardware store or wherever they sell lengths of clear tubes. Go for two dimensions. The smallest tube should have an inner diameter of 4 mm (to fit the outlets on the bike). This is the one that is pushed into your vacuum outlets on the bike. The other dimension will have an inner diameter that matches the outer diameter of the thinner one. In my case the larger one was 6 mm inner diameter
'Building':
The goal is to allow the larger tube to hang down from your ceiling in a U shape, and you fill it with two-stroke oil (it's colored and if you screw up it's made to handle being sucked into the engine.)
Allow the larger tube to be apprx. 5 meters, This allow for the U to be 2 m tall and then 0,5 m at each end where you connect the smaller tubes. The smaller tubes are connected to the larger tubes, and (at least in my case) I just pushed one into the other, no need for any type of glue. The other end of the small tubes are put onto the vacuum outlet on your engine. In my case I used 2 x 3,5 m of length of the smaller ones.
The point is: You now have one long tube, larger diameter in the middle and with two smaler tubes, one at each end.
Allowing the center section to hang down from your ceiling in a U - shape, and you find some means to keep the two lengths hanging down close to each other will allow the oil inside the large tube to have the same level in both 'legs'.
As each 'leg' is connected to one of the cylinders, any time there is a slight difference in vacuum between the cylinders, this will immediately show on the oil level between the 'legs'. I allowed the level to start at the middle of the tube, allowing for +/- 80cm of level change. That was plenty.
Is it accurate? You bet. I built one in order to sync. the carbs on my 90S. You could barely touch the adjustment screw and it would show.
It is my humble opinion that you are not able to get a more accurate way of sync. the cylinders, and the total cost was less than £20.
A but cumbersome to rig, but once I was done with it I coiled the tubes for storage, with the oil inside, then I connected the two open tube ends with a leftover from the larger tube to seal it off.
(and you will be in trouble if you want to test the bike on the road while performing the sync
)