Up until now I have used OPT and found them great. They even paid for return of an eyepiece, a Pan24 that was faulty. They stuffed things up a bit returning the new one but. Something I found out re customs is that if you get something in for less than $500aud you dont pay any duty or GST. This I found out the hard way only appears to apply to stuff bought in via Post eg USPS. My return eyepiece came back via express courier and unknown to me the cutoff point is $250aud. So I got hit by customs. This I thought was a pain in the arse as it was a warranty replacement, but you cannot argue with the Aust Customs Service. I am at present negotiating with OPT as I did not request a couriered return, and in any case they put "gift" on the package which also raised the red flag at customs..
You live and learn