In the same situation I found ROS was a really handy way to do my tax return -- wouldn't change to anything else now as it's a reminder to pay all the right stuff and claim the right reliefs (though I don't have much of either any more). The only downside from your point of view is that if you fill in a Form 11, Revenue will probably mark you as self-assessed for income tax, and will expect a Form 11 every year until you tell them to take you off it. If you don't want that to happen, you can just fill in a Form CGT 1 and a Form 12 which (I think) should cover capitals gains and dividends between them. To be honest, though, once you've filed your first return online it takes about 20 minutes if you have nothing out of the ordinary.
Just one important thing to note -- if you had a capital gain last year, you were due to pay the tax in either November or January last depending on when it accrued, even though the tax return (which is just the accounting side) is not due until October. Revenue will charge you a 10% penalty for late payment.