I wanted to add my problems here as I switched to Three mobile broadband in December and all was fine, now (over the last week or two) I am having serious issues with the 4G broadband.
NowTV and Amazon are slow and sometimes won't even connect, Amazon music doesn't work fully on my Sonos system now either.
I tried everything to try and fix it and the only thing that does is a force to 3G (I have the B535 router).
When on 3G I have no problems whatsoever, everything connects fine first time the only issue is it's half the speed of the 4G.
After noting the issues above I have just tried the fast.com speed test (Netflix powered) and speedtest.net - fast.com 2.5mbps, speedtest.net 20mbps
I can't work out how they can stop the 4G working properly but 3G works. I have complained and they are 'investigating' the problems so I'll await any answer from Three.
This looked to be a perfect solution to my slow broadband (we can't get FTTC here) and now I'm regretting it, thankfully I opted for the 30 day contract.