Make sure you take a copy of the parcel charges with you - though it really shouldn't be necessary.

My LPO has been happily working with the new system since it was implemented, and are liking that they don't have to measure parcels and type in dimensions when the weight is under 5kg.

Something else I was told by my LPO.  The plastic satchels are now only graded in small, medium, large and extra large.  And you can put up to 5kg in any of them now.  So you only have to buy the one that fits what you are sending.  Much better than the old system where you were limited on weight.