Operation in client mode as a pure access point is of course possible. However, as already mentioned in one of my reviews, seamless roaming is no longer possible; this only works in repeater mode. Deactivating the LEDs is not possible as far as I can tell, at least I cannot find any settings for this in the web interface of the device.
Yes, the second picture is a bit confusing with the socket. However, the plug on the back is an ordinary two-pin Euro plug, like the one we use.
Attached is a picture: http://jordancomputers.com/images/thumbs/0008463.jpeg
More information about the Euro plug: https://de.wikipedia.org/wiki/Eurostecker
I have a home network that should offer seamless roaming with LinkSys components, there are 3 LAN APs and 3 extenders (all as required with the same SSID and security settings and the 802.11r protocol enabled).
However, the clients must also support this protocol, which depends on the model, the network interface and the drivers - you have to find out for iOS, Android, Windows, Linux, etc.; on my S9+, for example, "aggressive WLAN handover" must be activated in the developer options). On a 1st generation Surface Book, the Marvell AVASTAR adapter does not have a setting for 108.11r, but it seems to work quite well.
In operation, I sometimes see this and sometimes that with the S9+ - i.e. there can be uninterrupted streaming or phone calls (VoLTE) when changing floors, whereby the device is then actually connected to a new AP - but sometimes the device also remains "stuck" to the previous AP or extender, although I am directly in front of another one...
According to LinkSys, a MaxStream router provides the central control for seamless roaming, especially in order to place the devices optimally.
However, since success is not guaranteed even with all the necessary components and settings, and since not too many clients support the 108.11 r protocol so far, I would not expect miracles at the moment.