A little late to the party, but I run 800 of those things on my Christmas tree with a Pixelblaze and an output expander and I like them a lot. They make pretty light, don’t show too much wire, and are easy to bend into place.
They are indeed fixed address. Cutting them without keeping track of the original relative positioning can make very weird things happen.
(You can use this property to make more-or-less mapped sculptures without using the Pixelblaze’s mapper - here’s the original discussion thread.)
The major electrical issue I’ve had with them is this: the wire is very thin, and the insulation somewhat fragile. It’s definitely possible to short them out with enough bending. You’ve also got to be careful when soldering not to vaporize the insulation too far up the wire. Once started, it goes away fast!
Another thing that you might want to check is that all your grounds – everything going to the LED or to the Pixelblaze – have solid connections to each other. These lights are very timing sensitive, and might also be sensitive to minor differences in ground level.