Last fall I order a large quantity of these plastic air layering balls on ebay:

Thought I'd give them a try...
Kevin
We tried the smaller ball and it failed in 100% of air layers
even on species that layer willingly. though my air layer success normally is pretty high. I saw larger ones on Amazon but decided to continue the old fashioned way.
Satya, those balls worked for me super well. I got 100% successful air layers from them so far but you have to control the soil moisture carefully because of the openings on the top and bottom for the small and medium size and the large size has additional openings on the sides. I’ve had success using all three sizes.
I’ve been air layering for quite a long time and the traditional method takes longer but doesn’t require as much up keep because everything is sealed up and there is little moisture loss. With the traditional method, the initial watering is usually enough to get the air layer through till harvesting/removing from the tree.
These new air layering balls are faster but not for those that don’t have time to check up on the condition of the soil inside.
On hot days, the smaller balls can dry up very quickly.
I moisten to field capacity for the initial fill and then re water once soil moisture is about 20-30% approximately.
Here’s an air layer I recently removed

This is the smallest size.
Simon
Hi Simon, sorry didn't see your answer until now! Wow that is a nice root ball! Yes I noticed they dry up too fast, and had no time to moisten them, that's the reason mine failed and that's the reason I stopped using them. I travel a lot so cannot consistently tend to them unfortunately.
As for Suriname cherries, I have one seedling tree that outperforms every other one I have; the fruit is very sweet with less acidity than a typical Suriname cherry and less gasoline flavor; Zill dark are much tarter in my garden, I have maybe 10 trees and this one is sweeter/larger/juicier than Zill's. It's orangish-pink in color and has a very distinct long neck. I shared seeds with many friends, hope someone grew them to see whether these qualities persist. Let me find a photo...