I've used a Protrail extensively for two years. I backpack year-round in Colorado, including archery and muzzleloader hunts. The Protrail is excellent. Super light, easy to set up and durable. I've used it during all four seasons.
For archery hunts, I find that around mid-September the nights start getting a little colder, especially if you're near timberline, and then condensation can become a big issue. Because the Protrail is a single-wall shelter and so small inside, you stand a large chance of brushing against the walls and getting clothes or quilt/sleeping bag wet. Also, the mesh near the bottom of the tent tends to start feeling drafty when it gets colder - there's no way to stop those cold breezes in the Protrail. I got caught once in a cold rain cycle that lasted a few days, and the protrail was livable, but barely, as the interior never dried completely. But, if the forecast calls for dry weather in September, it's a great little tent.
I will continue using the Protrail during the summer and early season, but I'm getting a double wall one-man model from TarpTent for late September hunts - maybe a Bowfin or Notch.