I haven't used it but just had a read through
this.
Point b on that page seems to indicate that watching browser streams will be more trouble than it is worth. eg. To watch even Youtube you have to reconfigure the Tor setup.
I would imagine that the BBC iPlayer would require reconfiguration too, and that's supposing that the iPlayer recognises the IP address provided by the Tor network as a UK IP.
You pass through the Tor network so any effects on speed would depend on the network capability and amount of traffic on the network.
It appears to be designed for people wanting secrecy, whether from state snooping or to stop websites knowing who has visited them but appears to require a lot of conscientiousness on the user's part at all times, even when accessing other sites while not using Tor. The need for secrecy would have to be very high to make it worth the effort.