Is it good to get Synthetic Hair Transplantation? What are the pro and cons ?

Synthetic hair transplant is not approved in the U.S. There may be numerous health issues associated with synthetic hair. 

Synthetic hair comes with a long list of side effects and complications, including a virtually 100% infection rate. I was strongly, strongly advise against a synthetic hair transplant, and look into FUE or FUT transplants instead.

In my opinion, people with hair loss should stay away from synthetic hair implants despite the glossy ads, testimonials and manufacturers promises. I have seen so many patients lives ruined by having this procedure done and then developing widespread inflammation, infection and even scalp necrosis. To be a successful long term solution, the implants would need to be biologically inert and although there are some new synthetic hair producers that make this claim, I have yet to be convinced. It may seem like a great solution especially for patients with extensive alopecia areata or those with insufficient donor for a hair transplant but my advice is to avoid synthetic hair implants. 

it is just chemical , a kind of continuously irritating substances  that you contact with your scalp skin and much more expensive than a hair restoration surgery . So would you like to have it ?

Simply, stay away from it.   It will lead to scarring of your skin, further loss of your hair.