The mechanical emitter uses a chamber which fills with water then dumps it out at preset intervals of time. Much like filling a cup with water and then pouring it out. I haven't seen a mechanical emitter in years. The last I saw was a prototype at a university in the early 1970's. There are two basic categories of drip emitters, pressure compensating and non-pressure compensating .
All emitters are pressure compensating to some degree, that is the purpose of an emitter.
So you can't determine what is pressure compensating by the manufacturer's literature, almost all make that claim. Pressure compensating emitters are designed to discharge water at a very uniform rate under a wide range of water pressures. As far as I know they are all diaphragm type emitters. Non-pressure compensating emitters are also designed to discharge water at a uniform rate, but the water pressure needs to remain relatively constant or the discharge rate will vary. The best method is to cut open an emitter and look.