What features are not available if running ASUS routers in AIMesh AP mode?

[GawainXX2]

I'm considering purchasing a security gateway and placing my Asus routers from Mesh Router into Mesh AP mode.

In addition to VPN, what features would I be looking at losing?
I'm aware that I would lose guest Wifi but would I still be able to have multiple SSIDs?
Will the ASUS phone app still connect to the router?