The tool linked above is just a screwdriver and it would have to be a pretty special screwdriver that I expected to use very often before I would pay that much for something so ordinary.
You need a screwdriver and a wrench to balance the carbs (plus vacuum gauges of some type) and the wrench has to be a type that allows you to hold the screw with the screwdriver while you tighten the nut to lock the screw in place when you are finished.
I can't say for sure about single tube backbone frames but it is possible to use an ordinary box end wrench and an ordinary screwdriver for balancing the carbs on bikes with the triple tube frame. I did it on my GL500 the whole time I had it and on the CX650E based machine I have now for several years.
But it is a bit awkward so eventually I wanted a better tool for the job. Tools similar to what I made are available for sale and aren't terribly expensive if you expect to need one on a regular basis but I only have 1 bike that I would use it on and that doesn't need the carbs balanced every year so I decided to make my own from what was available.
The dimensions aren't critical. If the screwdriver you want to use is longer the whole thing could be made longer as long as the tube isn't too long for the driver. My screwdriver is long enough but the tube I used (which is what was available free) is about as short as you would want (at least with the triple tube frame) and could have been 1/2-3/4" longer with this screwdriver.
Note that I chose a cheap screwdriver that I seldom used; I don't need to balance the carbs very often so it is perfectly adequate for the job and I don't mind leaving it with the tube so I can find it the next time I need it.
Some of the versions of this tool on the market have an arm welded to the tube for turning it but I felt it would be better to use a nut and turn it with an actual wrench.
To use it I put the socket end on the nut, a 7/16" or 11mm box end wrench on the nut end and slide the screwdriver through. Hold the screw with the driver while you use the wrench to loosen the nut 1/4 turn or so, then balance the carbs per the book and finally hold the screw with the driver while tightening the nut.
As an aside-Check what clearance you will need and what length tool will work best...the flexible ones I use for hose clamps on inline fours
You can also get 1/4" metal flexible drive extensions that are useful for both nuts/boltheads and screws....that are more robust than those rubber flexi-drivers
This a premium brand but there is less expensive.
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