Description:
3 Watt T BIN LED
Rated @ 55 lumens
CR123A battery
2.5-hour Runtime (1:45 to 50%)
Input voltage: 1.5V~3.7V
6.5cm (L) x 2cm (D)
Made of Aerospace Grade Aluminum
Type III Hard Anodized Finish
Waterproof
Ultra Clear Glass Lens with AR Coating
Twist Head Switch

First Impressions:
The Fenix P1 is the smallest single 123 cell light I have ever seen. The fit and finish was very good, like all the other Fenix products I have seen so far. I like the simple design, and its output to size ratio is very high. I immediately attached a neck lanyard to it and started using it as a neck light.

Size/Weight:
I really don’t think a CR123 battery light is going to get much smaller. The head is just large enough to house the reflector and electronics. The body is as short as possible also, and the light operating by twisting the head, instead of a tail switch, has helped save room and make the light as short as possible.
The P1 isn’t too heavy at all, and is on par for what a single 123 cell light should weigh. I found that after a few minutes I was used to it being around my neck, and found it comfortable to wear.

Grip/Handling:
The P1 is actually easy to hold considering its small size. The flat sided body provides enough shape to keep a hold of. There is a large band of knurling on the head, so it is fairly easy to twist with just one hand. You may want to apply a small amount of lubricant to the rubber o-ring to make the head twist even easier.

Build Quality:
As with all Fenix products, I found the machining of the P1 to be very good. There are no rough or sharp edges. The threading seemed well done, leaving little play, and the o-ring was a good fit.
There are some slight rings in the surface of the reflector. But I have never seen this effect the beam on any of the Fenix lights.

Features:
The P1 is fairly simple in its design, which should prove to be reliable. It comes with a small belt pouch, and a metal clip that can attach to a small hole in the tail of the light. The P1 can also stand on its tail in candle mode, even with the small metal clip attached.

Output:
The output is rather impressive for a light this size, and the beam shape is very nice, with a fairly tight hotspot and nice smooth spill. The P1 is the brightest Fenix I have tested so far.
The LED tint of mine was very white also, no hint of green or blue.

Runtime:
The P1 will run about 2 hours in regulation before the output drops, with about an hour of diminishing light output after that. This is also the best regulation I have seen from Fenix so far. This means that you do not notice the light dimming over time. It is a constant brightness for the first 2 hours.
Here is a runtime graph done by CPF member Chevrofreak.

Heat Issues:
The P1 can get rather warm with long periods of use. This is understandable though due to its small size. I have ran the light for 8 to 10 minutes straight, and was still able to comfortably hold it in my hand. As with all lights, holding the light in your hand will actually help the light run cooler, as the blood circulating through your hand will hold to carry away some of the heat.
While I think the P1 would survive being left on, and unattended on a table, etc. I would not recommend doing this very often, as the heat can buildup, and may become hot enough that the light cannot be handled. Again, this is normal for a light this small.

Pros:
Smallest single 123 cell light so far.
Great Regulation
High output to size ratio
Good Fit & Finish
Low Price compared to other lights of similar performance.
Stands on Tail

Cons:
None so far.

Conclusion:
If you are looking for a small 123 cell light, that has great performance, and great regulation, look no further. The Fenix P1 is a very nice night and is easily carried due to its small size.
I recommend going to www.fenix-store.com for all your Fenix needs.
The site is ran by CPF member 4sevens, and his service is second to none.