To add to the other responses, synthetic hair will not look nice for as long as real hair. I have worn synthetic micros years ago, and after a week or so, the hair starts to get this frizzy kind of unkempt look to it and there's really not much you can do about it.
Synthetic hair is a nice, inexpensive alternative to human hair for some kinds of braid styles, but for the reason listed above, I wouldn't really recommend it for micros. Most people like to wear micros for at least a month and synthetic hair usually doesn't look nice for that long with constant wear.