Waz,

Sorry, I don't know any site to this topic.
I only have my own experience: Once I grafted a tubercle of Ario bravoanus on Echinopsis and it took. 2 years later two growing points appeared out of the cut surface of the Echinopsis about 3-5 mm apart the base of the tubercle. These growing points developed into two heads of Ario bravoanus eventually.
I guess one should cut the tubercle as close to its base as possible when grafting or rooting it, which also is possible.
Grafting tubercles with areols on its tip of other cactus genera is also possible and usually results in a new plantlet developing from the areole within half a year.

Jordi

Jordi,

2 years is a long wait. I'd have faster results grafting seedlings. I am sure faster results are possible. It might have to do with knowing where the vascular bundle of the tubercle is and matching it up on the V.B. of the host.

I have tried grafting with the tubercles of a dying (stem rot) of an ariocarpus seedling. Will see soon how long I'll have to wait.

Waz

Waz,

I am not so sure that faster results are possible with an Ario tubercle. Unless you are able to graft a tubercle with at least a small part of its axille. Otherwise new buds of growing points have to be developed which takes its time.
It goes without saying that the VPs of scion and understock have to meet in the first place, if not, the scion will dry up soon.
Grafting seedlings instead of tubercles is a much faster and the usual way of propagating Arios, of course.
Jordi