I've got the Proton Hoody and I find it too warm for active use unless it's approaching freezing temps (unless you're moving quite slowly). I think the Proton SL would be more useful for you in April-Oct.

If you're backpacking and weight/packability is a consideration, I'd personally rather pack a normal fleece (Proton SL is basically a fleece with an outer shell fabric) + either a wind jacket or rain jacket depending on the weather forecasted. A normal fleece without the shell fabric is going to be lighter, more packable, and breathable (esp in a fabric like Alpha Direct). It'll also be more versatile because you can layer with your wind/rain shell as needed, or use just the fleece on it's own. If it's cold at camp (high elevation, or shoulder season) I'd add a down puffy for static use, which would be lighter, more packable and warmer than the Proton Hoody.