I suspect most of the FETless electrets of this type of construction are simply variations of the Chinese ones like this:?
which are often actually quite good. Usually a bit noisier than 34mm? non electret? LDC capsules, but not too bad.
The JLI data sheets don't help much, they're just mostly 'copy and paste' nonsense? ?(2k2ohm 'impedance' for a FETless electret?? )
Some electrets with that kind of backplate structure have grills across the front - some not.? Those that I've had from Aliexpress don't sound too bad.
Certainly very good value for money.....
