I have a C102HD on the Celestron CG-4. It would work as a teaching tool for learning setting circles, but I also have a C8 on a fork mount. I'd much rather us the larger circles of the C8 if it was my choice. You might want to consider a C8 or an 8" Meade SCT (used on this site are available for a little more than your stated cost). It depends on how much you (or he) will depend on those (smallish) setting circles. The SCT circles can be used with the vernier, but the CG-4 circles are so small, the vernier would probably be questionable. (I confess, I haven't tried using the CG-4's circles yet as it is my newest scope/mount).
Clear skys,
Ed
P.S. Setting circles only work well if one has the patience to level and polar align the mount/ scope really well. I have become spoiled by my telrad books and 1x finder. I just rough align to polaris and start pointing at bright objects. Just an extra $0.02.