I have used shelly 1’s, they control one light (or set of lights). The shelly 2.5 has two relays, so better fit if you have two switches under the same plate to control 2 lights (or 2 sets of lights)
Francis nailed it here. If you have multiple switches in one electrical box (most common in areas that have multiple light switches), I would suggest using the 2.5 to use less room; However, if you have multiple switches in different locations and electrical boxes (not common), then I would suggest using a few shelly 1 devices to control the lights. In my experience, I have used a few shelly 1 devices in the same electrical boxes and the volume is very limited so the 2.5 would be the best way to go.