Your method with the bars would allow you to set both to the same but it won't ensure that they are set to the zero line. How about you repeat the process but with bars on both the top and bottom. Then set it so that both the top and bottom distances are matching. That'll mean that your ailerons are set to zero or near enough. Also to avoid errors due to angles make both bars the same length and long enough that the ends are very close to being vertically in line with the leading edge. A little out either way won't matter because if they are both the same distance you'll still be able to center the aileron to the wing with a good degree of accuracy.

Oddly enough the Robart guage won't help you actually center the ailerons. It'll let you set them to the same angle but that angle may not be actually centered. unless you can put one on the wing where it centers on the hinge line and the other on the actual aileron. But few models have a gap that would allow that.

You can do the same on the elevator and rudder but I've always found that just eyeballing them for neutral was close enough.

Now if all this was for the actual alignment and glueing the wing and stabilizer into place then I'd want to do things to a much greater degree of finess so I knew that the model was all set up nicely to 0-0-0 to within less than 1/2 degree. Ideally to within less than 1/4 degree. But for just setting the surfaces for the first flight your method but with two sticks will work just fine.