I think it depends what time of year you plant the stool. If it's put in towards the back end of the year/late summer, then it has a chance to become established before the following summer and the stalks will be a reasonable size. If the stalks are less than the width of your thumb don't take them, and let them rot down into the ground. Rhubarb is greedy and will need feeding - a bucket of well rotted manure on top of the crown at the end of the season, some rich compost every two or three weeks in season, and don't forget to give it a drink every now and then. If it bolts (flowerheads) take them off and give it a good drink of water.