OK, I just conducted a peer-reviewed empirical study on the field (ie, I peeled one while my wife was watching), and I can state categorically that:
* the skin of the #kumquat is bitter (but not much, less than an orange's)
* the flesh is quite acid and a bit sweet
Case closed. It's quite good.
Bonus: try with #coffee (eg, eat kumquat and while the flavour is still in your mouth, move to coffee). 😋