Check out irrigatias. I've been using them for some years to great effect. In Australia at the height of summer a 100l reservoir needs topping once a week, you can expect much less
Those sorts of thing sound great for watering a few pots. Could probably work well for the rhubarb with a dripper somewhat near each plant and under the shade of its leaves, they they are large and spaced out. Attempting to grow some tree kale which could probably use it too. I presume you balance the drip rate to keep the area of soil moist but not soaked.
But I also have things growing that are spread out more like walking onions, garlic, jerusalem artichokes. There isn't really a clear point to water for these and they take up a fair sized area.
I've run these on full beds using sfg, one dripper per square. The larger model (c60) actually waters three separate 13mm dripper lines set up in rings around the base of 20year old apple treas
(Err, not sure that made sense: three trees, each has a large 13mm poly dripper ring around the base. The c60 feeds all three simultaneously. At my previous house it actually watered three seperate beds - two 2x3m , one 1x1m)
I have a C24 watering a 1x3m bed with a banana tree. You can get a lot of water out of those buggers and you can tweak higher flow dribblers and 4mm weepers
Permaculture theory and practice