It's also known as spice, used to be legal here too. At the time it appeared the police was giving us a very hard time finding the real stuff, so we took a legal alternative. We kept going for almost an entire year, and from my experience, it diminishes the high of natural marijuana when smoked regularly. When it became illegal, one of my friends had a short-term depression of maybe a week, but after that everything went back to normal. The thing about spice is, the high lasts from 30 to 40 minutes max and after that, you feel like you haven't slept entire week. The only thing I like about it is that it takes a very small amount to be effective compared to natural marijuana. But the high is shorter, the stone is way stronger and the fact that if I smoke it in the morning I'm literally a zombie whole day made me despise the thing.
The reason it became illegal is because a lot of people here actually died from it, as they would take the entire package (3g) and smoked without mixing it with tobacco in 2 joints. As a long term marijuana user, I think you're better off taking some time to find the natural stuff instead of smoking this. Be careful with it, if you overdo it spice becomes a really nasty thing.
Spice... some people call some other things spice. Elven spice. Anyhow, I hear that synth weed is not nearly as good as the real thing. I, of course, can't speak from personal experience, but I would (and do - for those rare occasions) stick to the natural thing.