Which is the safest hair extension method on fine hair?

Without a doubt it's a micro rings method,silicone lined or shrinkies

I agree. I have fine hair, and I have had extensions several times, using a variety of different methods. I currently have micro rings, and they are great for any hair texture because they are so fine, almost imperceptible. That said, with fine hair you must be very careful. All methods of hair extensions attach a large quantity of extension hair to a relatively small amount of your own hair. Even if the individual extensions are small, as they are with micro rings, you have an unnatural amount of weight added to your own hair. This can result in your own hair being pulled out as a result. You will always hear that 'hair extensions are damaging'. An HONEST stylist will admit that this is true, in all cases, and this is why.