Grimlock248
Head-Fier
Fair points, and the differences can be looked at further here - https://crinacle.com/graphs/iems/graphtool/While the Massdrop Plus are generally nice IEMs, they are quite substantially bassier than the ER-4S/ER4SR/ER3SE/ER2SE, and also still a good bit bassier and warmer than the ER4XR/ER3XR as well (around 4 dB stronger bass compared to Etymotic's single-BA XR models), and also warmer in the root/fundamental range when compared to the ER2XR. They're more in line with a "warm v-shape with accurate mids" (due to the slight upper treble boost that they have as well) kind of tuning, and boast Campfire Audio Andromeda/NocturnaL Audio Atlantis quantity of bass, but with less thick lower mids than those.
The Plus recommendation was halfway recommended because it's the iem that best fits/conforms to my ear without sticking out. I can't think of a better one to fit under a hat, as the other poster mentioned.