Excellent trail - one of my favorites! It's definitely a good workout (pretty much straight uphill the entire way to the butte), but so worth it for the views at the top of Stein Butte. It is black bear country, so you will want to talk out loud to let anything know you are coming. Also, beware of ticks in the spring months of March - May. We went the first weekend of April, and had some issues with ticks. In my experience, they normally don't recede until June.
It's roughly 5 miles from the start of the trailhead to the top of Stein Butte, and you also have the option of making a more intense (albeit slightly shorter) return trip by continuing on the trail that winds past the butte and descends STEEPLY for a few miles past a couple of old mine adits, before spitting you out onto a Forest Service road (which you can then walk along back to your car).
Great trail. Well maintained. Exhausted after but it was totally worth it. We went this month (March) which was accidentally a really good time since it was the perfect temperature. Unfortunately I wasn't expecting the ticks to be out in full force and I pulled over 20 off of my dog, fortunately only two stuck. So be prepared with a tick collar or something for your canine pals. Other than that loved the hike!
This trail really felt strenuous. I think perhaps because it is relatively short (3+mi to the summit) it is rated moderate but it feels harder than that. The views of the surrounding mountains were spectacular. The Applegate lake was pretty. other than those two, it was a steep trail in our beautiful Oregon wildness.