You must choose WiFi client devices very carefully to have real use of three-chain WiFi AP, because most of the WiFi devices, even iPhone11Pros and some of the latest MacbookPros have 2-chain WiFi: https://www.duckware.com/tech/wifi-in-the-us.html
-cAP AC is ARM processor based, with a very powerfull processor. It has low antenna gain (omnidirectional) and should be mounted to the ceiling. It's not wheater sealed, to be used indoor. It is very similar to the hAP ac2 , in a different package.(hAP ac2 has more ports)
-wAP ac is indeed a good omnidirectional AP, with low antenna gain. It has only one ethernet port.Is wheater proof, can be used indoor and outdoor.
-Omnitik AC is designed for outdoor use. It has 7.5 dBi antenna gain (radiation distribution is donut shaped around the antenna, it will (send and) receive over a larger distance in that direction). It only has the 5 GHz band, and is limited to the outdoor frequencies (5500 MHZ and up) in the European regulatory domains. It has more ethernet ports, USB connector and there is a PoE model.
What are the differences? They seem the same on paper, 2x2 802.11ac APs.
Not so much performance, but environmental, connectivity, and decor.
OmniTik line doesn't do 2.4GHz or wall-mounting, and offers multiple ports which can be had with POE-out; cAP AC is not an outdoor unit, and comes with two Ethernet ports; WAP works outdoors, has only one port, and optionally comes in 2.4GHz.