I've been doing that journey since the end of September.  The barriers were installed shortly thereafter, but I have not seen them operational once.  I arrive at the station  around 11 am and return again just after 9.30 pm, so I guess they switch them off when they see me coming! 

I travel from Ashford International to Bristol Parkway and back once a week.  I buy advance purchase tickets and on several occasions have had to change the date, which has meant buying an excess ticket for the journey.  Without fail the excess ticket does not work at Paddington (or at St Pancras for that matter) but does work at Ashford, Bristol Parkway and at the Tube stations.  I usually avoid the barriers at Paddington though by accessing the platform from the footbridge (although the barriers they've recently installed there will no doubt be operational soon).