I have used both the Ferrino Trekking Raincoat and current use the Sea To Summit Ultra Sil poncho. SYates is spot on about the reflective layer. It DOES keep you warmer in cold weather, but likely too warm in the late spring and summer months.
IMHO, a poncho is better than a more enclosed trekking raincoat, like the Ferrino. It is lighter and better ventilated. Still, any waterproof cover intended to protect you from wet stuff falling from the sides is going to contain perspiration. The more watertight it is, as in a pants and parka suit, the wetter you and your backpack will be. The trekking raincoat has a reflecting inner lining and also does not have adequate ventilation, at least IMHO.
A poncho overcomes most of the ventilation issue. A backpacking / hiking poncho will cover both you and you pack adequately. But your lower legs will still get wet. To counter this, I recommend wearing nylon or other fast-drying zip-off bottom hiking trousers. When you reach your destination, you can easily rinse out the lower pants legs. The usually dry enough to wear again in less than one hour.
My biggest gripe about the S2S poncho is the plastic snaps. They separate easily in a strong wind or with movement. I have been experimenting with various alternative to keep the snaps closed. I used duck tape on one Camino. That sort of worked, but the tape tore with movement.
This year, I used 3M reflective tape to hold the snaps closed. The snaps still came open, but the tape kept the poncho from billowing out in the wind and rain.
Still not a "perfect" solution. My latest notion is to just super glue them closed (snapped) as I never use my poncho for anything but rain protection. But that is an individual decision. I am still thinking on it...
I hope this helps.