you will hear comments either way. i say save up and get it done professionally. i tried to help a friend install some. the ebay kits are cut correctly and they come with deceent instructions but it is a pita....
Years back when I was going to tint my Honda, I contemplated doing it myself for a fraction of the cost by buying the precut pieces on eBay. I talked myself out of it and have it professionally done, I didn't want to take any risks.
I have a friend that has done it many times and he says it's pretty easy if you have patience and follow the correct methods. He offered to help me install the tint but I passed.
Heres one tint installation guide, there are many others on YouTube