Can't recommend one enough. We have a DIY one from an old orange pulp barrel from Spain which collects from our roof via an in-line rain diverter valve - these are very easy to buy and fit, then forget.
Things to think about - put a lid on, help prevent midges breeding in there although they will anyway. Needs a tap near the bottom. Positioning of barrel - ours is elevated and stored on a flat roof at a height of about 1.5m (I'm an engineer and made sure the support was adequate). This means I can fit a hose on the tap and use gravity to help me move water about the garden. If you buried it, you'd have to pump the water back out - quite possible with a hand pump but laborious.
We use ours for watering all our seedlings etc.