I use them because it's the best that's available at the time.
I use these to freak out bicycles. They work well once you have them in place. Be warned they are fragile! Battery life on a dollar store battery will definitely last you one night of riding. I get about 6 hours of good light out of Dollar store batteries. I've done seven bike builds using them. You can solder strands together. It takes away from battery life but gives you a more consistent flow when you have them in certain modes than if you use multiple on the same project because they will lose sync after a little bit. If you are just going for one color at a time solid lighting you can use multiple on the same project with no problems. If you use strip lighting the issue is the stickiness or lack thereof.