The taste far, far exceeds anything you can buy, even the most expensive vine tomatoes. Also, you have no air miles if that kind of thing bothers you (even Irish grown commercial tomatoes will have some carbon footprint as they're grown in heated, irrigated greenhouses to get a headstart). In addition, you know that they haven't been doused in every chemical under the sun.
I take it you've never eaten a tomato straight off the plant - once you taste one the first time, I guarantee you'll grow them every year. It's the one vegetable I would never not grow myself. They're easy, pretty much labour free, and highly productive.