Mangoes are super diverse - dozens of them on markets in Southeast Asia. Bananas - damn crazy diverse fruit (with different tastes)... I recommend visiting 1) the plant market in Chatuchak (on Tuesdays and Wednesdays as I remember) and especially 2) a plant fair in Suangluang Rama 9 Park each December that lasts for 3-4 days. You can see many garden verities, and you can try some for free on the fair.

star gooseberry

As you said, not a goodberry at all. Secondly, nobody will understand you if you say "star gooseberry" - none of Americans or Brits. However, if you say "mayom" every Thai will understand you as well as some farangs living in Thailand.

There is another type of garden tree, quite common and looks like mayom - it's called bilimbi - you certainly have seen many of them. The taste reminds that of wood sorrel (кислица) and sorrel (щавель); would cool to try cooking sorrel soup (щавелевый суп со сметаной и вареным яйцом) with it.