Thank you good to know. Full HD is good video quality ill grab chromecast when ill need it.Casting will go up to whatever resolution the TV/media is capable of, or whatever the app itself allows. In Prime's case, it casts to 1080p max. I believe BBC iPlayer is also capped at 1080p. YouTube can go 4K if the TV allows it. Basically you're not limited to whatever phone you're casting from.
The LG app can't grab 3rd party streaming content hence why it's limited to local files. Prime and iPlayer themselves will need to support the DLNA standard but big chances they won't spare the resources and will focus on the Chromecast standard instead.
I presume when ill use MHL adaptor it still wont show Iplayer content on TV is that correct cheers