I believe this is the same device as the EE Buzzard (sold as "in car wifi"), and a few days ago bought one - it seems to pick up a far stronger 3G signal than mobiles manage and the light goes to the light blue (or cyan as o2's instructions call it), which according to the O2 instructions is 4G signal, but the EE instructions claim it is "3G+ or 4G".
Not activated the sim yet as I don't believe I'm in a 4G area but another mast went live a few weeks back with coverage ending about 400m away so maybe just on the very edge if this dongle really is good at picking up signals as it appears to be.
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plusnet 80/20 FTTC
(and previously plusnet ADSL2+ Annex M Jan 2014-Mar 2015, Be* Jan 2009-Jan 2014, ZeN Dec 2006-Jan 2009, plusnet Aug 2004-Dec 2006, ZeN Apr 2003-Aug 2004)