I don't think there is one universal reason people would buy this battery pack. And that's the beauty of it, this thing has many and varied uses, to many to list. Mine is perhaps one of the more unusual ones, but perhaps after reading this there will be more people trying it out this way.Start with the fact that there are all kinds of battery packs listed here. But I didn't want to kludge around, I wanted to use it as much as it is as possible. That means charge it up, plug it in, and go. My use was to add two high power lights on my golf cart to help navigate hilly terrain when it gets pitch dark and those little flashlight bulb type lights that are mounted low on the front of most golf carts just aren't adequate. I got a couple of really cheap but bright LED lights that are designed just for this purpose, mounted them to existing holes in five minutes and I could have wired them to the existing battery terminal that already has a step down transformer from the cart's 36 volts but I didn't want to add to the drain of the batteries of an all-electric cart so I just ran the wire down the side of the windshield and terminated it into a standard DC connector to plug right in to this battery. One really nice feature of this is it has a simple rocker switch to turn it on and off and a simple built-in status monitor. When the battery gets low all I have to do is grab it off the dash and take it indoors to charge it up.PROS AND CONSThere really aren't any major magical things about this battery nor are there any big negatives. It is almost the size of my smartphone but about four times thicker. It weighs about a pound. When charged I measured the output voltage to be exactly 12.7 volts. They have apparently made a few design changes without telling their marketing department, such as they indicate there is an LED status light on the pack itself but that is covered with a blank plate and the status light is on the wall transformer instead. That doesn't affect operations in any way, it still glows red while charging and turns green when ready. They don't mention the five tiny lights on top of the case bit these tell the user approximately how much power is left.From their ad the company doesn't seem to be sure how this would be used either. That results in including a rather odd split wire dongle that has two male and one female connector. I guess they assume some people would want to charge their battery while it is in use, which is possible. Unfortunately it would probably have been more useful if they included a simple cable that had a male end on it and one that ended in bare wires for experimenters. That's not really a big deal though.CONCLUSIONThis pack works as it should, delivers the expected power, is small, lightweight and rugged enough for hobbies like model airplanes, drones, boats. The price is exactly what I would expect to pay. I like it and believe it earns five stars for all of the above reasons.