I have extensions right now. I have the keratin fusion kind (half head) and I've had them for quite a while. I absolutely love them! My hair is very fine and it never looks quite how I want it to, the extensions give me the thickness I need, especially since I do some modeling. I find them to be pretty easy to look after. I can't use sulphate shampoos, I need to be careful when brushing/styling/heat styling but other than that it's pretty easy. I go for maintenance every 6 weeks, which is free. Then I get them replaced or removed and put back in about once every 4-6 months.
Some people say that they ruin your natural hair but in my case, it's been the total opposite. My natural hair was very damaged and incredibly fine before the extensions and now it's thicker, stronger, healthier and shiny. However, I have had a weave in the past and it destroyed my hair to the point where I had to cut it all off into a bob.