I have a couple of them and they work quite well.
They work in ttl mode, but I prefer to just use them as "manual" slave triggers. Since I shoot digital, I just use the lcd to check my ratios. Before I had a digital camera, I used then with a nikon f5 and they did work in ttl mode, but you have to use them a while to get the hang of where to place them, etc.
And I have had no trouble getting them to work at further than the magic 23 feet. My understanding of the 23 foot limit is the "pre-flash" emitted for ttl dies off after that.
You still have to use either the built in on camera flash or a regular flash to fire them, but you can set the "triggering" flash to low output so the slave is predominant.