in some countries the Epirb is programmed with the MMSI number but in the UK there is a pre programmed serial number which you register - so if it has one i dont see why you cant bring it back - if theyare that much cheaper - do you want to bring 2 back???
I looked into this in the US. Some have a little encrypted image on the top that states country of origin - the manufacturer can change this with a laser for around $50 - or when buying in Oz ask for a UK branded one (shouldn't be an issue)
Bigger problem is that only the McMurdo one (I believe) is allowed to be transported on a plane as the others have components that are restricted for air travel (some sort of radio-active contents inside). However, any airline may be worried about handling it - it does look a little like a bomb to the untrained eye.
I decided the US ones, whilst around £100 cheaper, weren't worth the hassle once the £25 re-branding charge had been paid and the hassle with customs / airline etc.
Some EPIRBS are not allowed on aeroplanes either as cabin or hold baggage due to the battery type.Check with the airline and the manufacturer.
Is ther a big price difference
If you buy an EPIRB in Australia it will have an Australian prefixed serial number/MMSI and when activated, AMSA in Canberra will telephone to make sure it's not a hoax. Just looking in the past 2 minutes at a warning for those (you) who buy in Oz and intend to use it predominantly overseas. The warning and rego details are at http://beacons.amsa.gov.au/Buying_and_registering/Buyers_Beware.asp
Basically you won't get it registered because you can't supply an Aussie address, unless you've a relative here, but read the info for yourself from AMSA's website.