O I heard that this bulb can damage your tortoises eyes. How is that possible????

I believe it is because the coil bulbs give off UVB wavelengths that are so high (or low?) on the UV light spectrum that they give off UVC rays which are harmful. The mercury bulbs or long tubed bulb which give off rays closer to the middle of the UVB section of the spectrum which are safer.

I don't remember the exact how they do it, but they do. So play it safe and don't use them!

To get enough UVB out of such a small low power bulb, they were using a different phosphor, but it also emitted dangerous wavelengths in the UVC range. Also, it's possible that torts were staring at them because they're not bright enough for the tortoise to avert their gaze, but still dangerous.

Apparently they don't use the phosphor anymore, but I'd be more worried about a coil bulb simply not being an ineffective UVB source.

Coil bulbs, in my experience, work fine if you mount them properly. However, they are a lot more finicky than tube bulbs. Personally, I'd rather just use a MVB.