When I visited Guernsey in 1999 and 2001, I found you were more likely to be given their pound notes than their pound coins- same in Jersey, which I visited in 2000. I never received any of the Guernsey 2 pound coins in change so had to ask for some at the bank to bring a couple back for collector friends.
Guernsey and Jersey were the only places I've visited where there were three coinages circulating. UK, Guernsey and Jersey coins were all accepted as legal tender. The UK does not accept Channel Island coinage as legal tender, even though their coins are of the same value as the UK's. However, since they are of the same size, colour and shape, a few slip into circulation unrecognised here in the UK, as occasionally do coins from the Falkland Islands and Gibraltar.