I can confirm there is extremely heavy traffic shaping when using Three sim at feel-at-home location.
Have been tested it in Spain a month ago.
3 different sim-s, 3 different devices
2 pay monthly phone sim
1 payg sim in MiFi devices
Tested both spanish networks providing roamin with Three in spain
No difference whatsoever.
Small amounts of data using typical services working just fine or acceptable: e-mail, facebook, twitter, skype, short web browsing.
Once you start browsing picture-heavy pages - it slowing down. Almost to zero.
Same with facebook app - once you start browsing photos, it slows down.
VPN connection is totally unusable. You can establish connection, but is totally unusable, can't even access edge router settings
Skype video call is working with good quality though.
Same mifi device fitted with local sim (same network - Yoigo) is working perfectly.
Contacted Three via Facebook and they confirmed the traffic is shaped. Ooopsss.. sorry. They confirmed it's NOT shaped. They confirmed it's "managed" which obviously makes HUGE difference.