I have used the GSP from the UK a couple of times only. 

The delivery times were excellent...no complaints there but that is where it ended.

Both my items were paper/cardboard and were repackaged into cardboard backed envelopes with great big round stickers trumpetting that they had been repacked by the GSP.   They should have been ashamed to advertise the fact because the quality of the envelopes was absolute garbage and one was badly torn.  AP had to repackage that one in one of their clear plastic bags that they use for damaged mail.   This cost me AU$22.00....pricey but considering the number of sheets of paper in the package it was not too unreasonable.

The second item was similarly packaged but as there was less in it the envelope did not fall apart.  BUT for the same AU$22.00 I received one bookmark....heavy cardboard that had been laminated.

I consideredthat to be absolute piracy but as I was buying on behalf of someone else I just had to swallow it and pay up.