U Mic is a classic mira variable with a period close to one year, a reasonably stable light curve, and strong amplitude of more than five magnitudes in the visual (from 14th to 9th or better). Unfortunately it's also becoming less-frequently observed by visual observers as time goes on, which means the light curve is becoming sparser and sparser with time. The problem becomes especially acute if instrumental surveys aren't able to pick up where the visual observers leave off, or if they themselves stop observing after visual observers move on.
Among the variables of sparse Microscopium, only R Mic was deemed well-covered enough to make it onto the AAVSO LPV Program, and no stars from Mic made it onto the Legacy List. But that doesn't mean observations aren't worthwhile. The AAVSO created the Legacy Lists to ensure continued coverage of stars with historically good coverage as defined by the number of past observations. U Mic, and hundreds of other stars, didn't quite make that cutoff, but you can still observe them and improve their coverage. You can use tools like the AAVSO's Basic Observing Planner to look for Miras and other variables in need of coverage. Consider including a few extra stars among your observing list beyond what's in the LPV Program and Legacy lists. Future researchers may be grateful you did!