If you buy simply on features/price, you may miss the benefits this battery pack has to offer. Read on...
This is my second IMP50D, I managed to leave my previous one which I had bought a year ago, on a plane.
I had been very happy with the previous one: without having done specific testing, it seemed to provide the expected recharges (mainly being used to supplement my underpowered big-screen phone).
Benefits: It recharges fast (very important 1A output, compare others' maximum output)! Also, if the phone (at least) is charged, the power pack no longer drains - a very important detail, NewTrent have spent time developing this logic, and it works great. 2 USB outputs so you can charge 2 phones/iPods etc.
Good, convenient size, well thought out cabling too. It comes with 2 adapters that allow you to charge the pack from the PC's USB, and to charge your appliances either via mini-USB or micro-USB. Of course, you can just plug your iPod cable into it as well.
This model represents for me a good trade-off between cost, size/weight, and convenience. If you want, there are power packs that more than double the 5000mAh rating, but this is the equivalent of 3x charges of my phone battery.
With my second one, I had the misfortune of getting a faulty cable - I got in touch with NewTrent, and a replacement cable set was delivered within the week. Impressive customer service - I thought I would have to return it via Amazon, which is slow & costly. NewTrent gave superlative service, took note of the issue and resolved it the same day (international postage took care of the rest of the time).
Conclusion, well designed and well executed. A great company to deal with. Look beyond the price of the 2000mah battery packs, they will disappoint you - this one won't.