I've got 10 or 11 on my layout and, as with others on here, have suffered a number of failures.
My layout is DCC and the signals have been set up using Train-Tech SC3 dual signal controllers, the failures I've encountered have mostly been of a mechanical nature, where the activation mechanism in the base of the unit has "given up the ghost".
I did replace the first failed unit with another but as more and more have packed up I've decided to live with them as static units until I get around to powering them via a servo-type approach - current thoughts are to strip the base apart and activate the signal using Cobalt digital motors, which would have the added advantage of the signal "remembering" which way it is set.
That's been another annoying "feature" of these units - that they don't know if they are on/off - even with the train tech decoders they end up out of sync with the layout control panels.
A pity really - nice idea is but the design and execution sadly lets the product down, I shan't be spending any more money on them....