There are no country restrictions as such. Although, if you bought the topo versions (eg etrex 30T), they will only provide the topo maps for the country they are being sold from. If you just buy the plain GPS unit, it will work here and overseas without problems. The issue will come from Garmin's limited warranty. I've never had to test this with any of my Garmin GPS devices, but Garmin will not accept "Online auction confirmations" for warranty verification. They need the original invoice from the store that you bought it from.
So if you buy from ebay, at least make sure you get an actual invoice/receipt for warranty purposes. The warranty is only for 12 months from purchase, but without the original invoice, they might refuse to honor it.
I've noticed that the etrex 20 price hasn't come down since the announcement of the eTrex 20x/30x and eTrex touch 25/35 series. The eTrex 20 price was floating around the $195 mark for a while, but it's been climbing up - most likely due to the falling Aussie dollar.
If warranty is an issue for you, have a look at this mob from NSW
http://www.nofrillsgps.com.au/garmin-et ... ndheld-gps I've bought from them before, and while the eTrex 20 is out of stock with them, if you preorder it, they include free delivery ($10 or so to Melbourne from recollection). Their price is currently $224.85, so just under $20 more expensive than the UK ebay option.
Once you get the eTrex 20 though, this is a previous post of tips on using it:
viewtopic.php?f=21&t=15200#p269919And a post on making a DIY bumper case for it
viewtopic.php?f=21&t=20683.