Behringer Powerplay P2

P2 is a much better than a P1 amp in both: size and power.

It is much more comfortable to use it for a standing setup, because, it is not as bulky as P1. If you make a custom cable 2 xlr mono > 1 xlr stereo it works as a stereo amp flawlessly. And thats the only thing that is better on the P1.
Power of the amplification and the power consumption is way better than it's bigger brother. 9v batteries on the P1, can hold not more than 1/3 time of this AAA battery setup.. Its superb. Quality batteries hold up to 10gigs (±2hours of playing thru the night) for me. While the P1 is not as loud and powers up on a single battery only for ±3 gigs..
It has a good headroom (much more louder than a P1) for playing with a loud band and setting up a powerful headphone mix.

2 things, that could (and should) be improved:

1: Though the format is small, its not very VERY strong. I have had used it for 30-50 gigs already, always clipping it to my jeans strap, sometimes sitting on a chair, sometimes standing up, and, it's chassis has a dent around a XLR area, and a belt clip has a little lost its form.
This does not effect its performance in any way. Just it could be a little stronger.
2: The batteries, more than a few times, after a transportation have had fallen from their places, so almost 2/3 times, out of 4, after you arrive at a gig, you have to open it up and reattach the batteries in to their place.

Price - makes it a no brainer.

Would I recommend them? Why would you even ask it! Would recommend it by 150%. It is a must have for any gigging musician. Just to have it in their backpack with a cheap set of in ears (for example KZ ES4), if the venue is too noisy/loud/not enough monitors/not working monitors - you can save your day for a ±50eur and hear everything loud and clear.

For the small sum of £30, it's just brilliant. Not all gigs I play where I'm using my in-ears need a wireless transmitter. This hard wired belt pack is perfect for smaller bar & pub gigs, even rehearsal rooms & home practise. No low end loss here, a perfect full range sound every time.
Using an XLR it works in mono only. The XRL cable also locks in to the P2 (so you won't accidentally pull out the XLR cable mid gig), as long as the XLR connector on the cable has that small locking tab. Most do, some don't. If you open up the P2 (like when to change batteries) you'll see there's a mono/stereo switch mounted on the PCB. In stereo mode you can connect a stereo jack cable and have a stereo mix. The jack doesn't lock in though, be careful not to pull it out by accident. Having the mono/stereo choice is fantastic.
Even though two AAAs last for many hours, I recommend getting rechargeable batteries & a charger if you're going to use the P2 a lot. Which you probably will if you buy one.
If you want to use in-ears, you need one of these. If you already have a wireless for your in ears, you still need one of these. Even just as a cheap back up in case your wireless battery dies in the last set of the gig, or to use at band practise, you need one of these.

This is a very compact personal in-ear monitor system and these are great IEM systems for anyone who does not need a wireless system.
BUT if you need Wireless IEM setup that don't cost hundreds or thousands euros, here is one TIP: DIY Wireless IEM "hack" setup to save extra money and portability on stage - three components that you need: Behringer Powerplay P2, some kind of wireless guitar system (aka Harley Benton AirBorne 5.8GHz Instrument or some similar cheap wireless transmitter options) and earbuds. Now you have your personal wireless IEM :)
So, this is a trick to save some money and I can confirm that the wireless receiver and the P2 behave very well together.

You can also connect a guitar to it and play with headphones, with these wirelessly hacked or with cable just for practice without disturbing anybody.
Of course, if you want the guitar to be wireless as well, you'll need another set of wireless.

One tip for mixers: if you use XLR to send a balanced mono signal from the mixer's aux, then set the switch to mono and the sound goes to both ears. If you are using XLR to send a stereo signal from the output to the headphones, then put the switch in the stereo position and it works as a stereo.

cons: the batteries sometimes come loose when you drop it or shake it heavily, I actually tape the batteries to the socket to fix it, no big problem

pros: batteries last a LONG time.. it says 10 hours.. mine lasts at least 20!... it's cheap (half the price of the Fisher Amp Stick (which it copies).
It sounds GOOD man. Really good. I also use it for monitoring in the studio.

If simple reliability is your goal for a headphone amp, then this is a good device to buy.

Pros:
- Sturdy and simple, can withstand the chaos of live performances
- Powered by AAA batteries so you don't need a separate power source
- Possibility for stereo audio
- Obvious how to open the device

Cons:
- Stereo audio requires purchasing a separate XLR splitter cable, and (as far as I understand) the signal will be unbalanced
- Not obvious how to close the device (the rotation of the chassis has to be aligned right, and in a live setting with poor lighting this may not be the easiest)