Configuring "dumb AP" (disable multicast snooping and IPv6)

I'm trying to set up two new LEDE APs and I'm following this guide here (I know the steps but wanted to make sure I wasn't missing anything with regards to IPv6).

The final steps in the process says the following:

Multicast forwarding is necessary for DLNA and UPnP clients to work properly. For example PS3, xbox, TVs and stereos use DLNA to detect, communicate with and stream audio/video over the network. Since multicasting is turned off (multicast snooping is turned on) by default in newer OpenWrt releases, it must be activated. This would forward any multicast packets to all ports allowing your TV to find your DLNA capable NAS with movies. In large networks, this could cause some overhead which may not be desirable.

Add this into /etc/rc.local

echo "0" > /sys/devices/virtual/net/br-lan/bridge/multicast_snooping

Now this does sound like something I would want (I have all sorts of multi cast discovery devices on my network. Mainly media servers and the like) but now I'm wondering if I should be doing the same on my main LEDE router. Is this something that I should be turning off in general? Why is it enabled?

I don't really want to be blocking anything on the internal network so any suggestions on how to do that would be great. I also want to make sure IPv6 works on both APs and that the devices connected to the APs will be assigned addresses from the main router / gateway. Is there anything special to consider with IPv6?