1. Solidly built. 2. Perfectly sized to take my Eneloops without crushing them. Any standard AA or unprotected button top 14500 cell should fit. Flat top cells and protected 14500 cells are unlikely to work, however. 3. Can be dismantled with a 2mm hex bit, making it easy to modify. Be careful to reassemble correctly if you do this. Some of the PCB pads are connected by tracks within the PCB, so you'll short out your cells if you get it wrong! 3A. You could bypass the springs and PCB tracks with flexible wire if you needed a high current battery carrier. 3B. You could also convert it into a Parallel 3 AA Holder by moving one of the springs so that they're all at one end and wiring the PCB pads in parallel at each end.