Similar (well, identical) computer HW specs (CPU, memory etc.). Main difference is in the antennas - LHG uses a 2x2 Mimo configuration with antennas more tuned for higher frequencies, ATL apparently uses a 4x4 Mimo configuration and adds 2x2 Mimo antennas for the lower bands. I've deployed LHG(G) routers successfully and highly recommend them. I tend to replace their modems with Quectel jobs though, for B28 or U.S. bandplan compatibility. While marginal (the 2x2 antenna isn't really tuned for B28), B28 compatibility would nonetheless be there.
I have yet to see and tear down a Cat18 Mikrotik device, so I'll leave my own question for the MT team or those who have seen the Cat18 line 'in the metal': is the modem mPCIe or M.2? Is Mikrotik fitting m.2 connectors to these routerboards?