If flowers are your thing, then do this trail now. If mosquitoes are not your thing, then don't stay overnight. :-)
We did this hike in perhaps the most leisurely manner possible, spending two nights at Buckhorn Campground and day-hiking from there up to the summit of First Brother. We let the hordes of day-trippers have the summit while we wandered another km or so along the trail to take in more flowery views. By the time we made the climb, there was no one else on the trail and we had the summit to ourselves. (OK not quite - we shared it with a chipmunk :-)
The trail is easy to follow, dry and very dusty. The flowers are blooming in every direction. The challenge is to name them all :-) It's quite a spectacular sight at the moment.
The bugs were moderately- to very annoying at Buckhorn. I didn't resort to deet, but a jacket, long trousers and bug net was helpful even if it did make sipping some wine a little more challenging. Mosquitoes consistently managed to find the hole in the back of my fleece. During the day, they were merely irritating, and would appear instantly at those few times the breeze dropped.
Buckhorn was a much nicer camping spot than I remember. Hard to believe it's been 7 years since we last camped here! Things to note: the outhouses have no TP - remember to bring your own! The food cache has the loudest, creakiest hinges I've ever heard - it can be heard from the other end of the campground.
Lastly, do I really need to burden you all with yet another rant about people walking on the meadows? Probably not. Sigh. ...