I thought I'd weigh in on this topic as I have what some would call an extensive amount of experience in this area.
Please note I have never ordered meds online, however the product I was dealing with is VERY similar, in both size, shape and detectability (i.e dogs, x-ray, noise etc.) and of course, illegality. You probably know what I'm referring to
Compared to other areas of Europe, Great Britain has an excellent success rate. It's WELL over 50%, I'd say 75-80% easily for small orders (10-20 small pills) and that's based on a lot of shipments, including the ones that weren't well packaged.
IMO the Australian Customs hype themselves up to near-mythical levels when their detection rates honestly aren't that great. When you read forum posts most people make our customs appear to be an impenetrable wall, with an officer examining every single package that comes into the country. In my experience that simply is not the case, and if you're ordering from a customs-neutral country such as the UK (or even better NZ/USA) with discrete packaging, most of your order is going to arrive safely.
I hope I could help, once upon a time I used to be a paranoid little bugger and now I have a good chuckle at Border Patrol.