I have planted more than 50 seedlings. Roughly half will be male trees that will never produce a fruit. The productive trees vary greatly but, in my case, it got some very good material that is sought after in our very competitive rambutan market. Most of the rest have been eliminated.
I have grafted rambutan and experienced a delayed incompatibility although that doesn’t seem to be common as grafting is the choice of most nurseries in Costa Rica.
But we use marcotting. You will hear that it’s not a good idea because the marcotted tree doesn’t have a good tap root. I have never seen the evidence of this being a problem. The lateral root system is impressive and, I think, helps the tree develop faster if the superficial soil is good.
Our marcots will fruit in 2-3 years.
Peter