Transmission spectroscopy metric (TSM) as a function of J magnitude for currently known transiting Neptune-sized planets around M dwarfs with a measured mass. The color of each point corresponds to its respective radius bin as defined by Kempton et al. (2018). Furthermore, promising targets that are above their respective radius-bin cutoff are labeled and marked with a circle, and those below the cutoff are represented with an upsidedown triangle. The uncertainties are only computed for TOI-1201 b.