I tried this kind of stuff one time, and it was terrible.
Long story short, I had open eye hallucinations and thought I was dying. Hallucinating wouldn't have been a bad thing if I had expected it and if it hadn't been really shitty/scary things. Also, my girlfriend is a nurse and was with me at the time and she took my HR because I thought I was having a heart attack and it was at like 196 or some crazy number. Worst trip out of any drug I've ever tried.. felt like I was forgetting to breathe :S
Apparently the feeling of dying or severe medical attention needed isn't uncommon on these synthetic weeds. I'd stay as far away as possible... just smoke the real stuff.
edit: Also, this stuff is hit or miss. I had tried it once leading up to the terrible trip, and it was okay, but a little strong for my tastes. That's with 2 relatively good bong hits. Second time, friend rolled a us a mix of the stuff and some tobacco so we didn't get super fucked up (about 50/50) and I took I think 3 good hits in a period of 10 minutes or so (pretty sure it was 3, like I said the trip came on STRONG).. honestly like 2 minutes after the first one I completely forgot where I was and just went with it. If you're going to do it, WHATEVER YOU DO make sure you maintain control lol. It's easy to say in the moment "ah, well I'm not really where I wanna be yet" and take another hit. Just pace yourself, if you're being adventurous, start with 2 hits then wait 20 minutes. If it's not enough, do another hit. My advice would be 1 hit at a time though, unless you take pussy hits.