Yes, it really works!
I self harmed and regretted it immediately. I went to the doctor two days after and she prescribed me bio oil which I used religiously for a few weeks. I literally applied it up to 10 times a day and within two weeks, the scars had faded dramatically. Now, a year later, they are gone completely!
As for stretch marks, it has faded mine a lot but they haven't disappeared and are still slightly noticeable. Maybe it is just me over analysing my body; no one will immediately stare at my inner thighs to look for stretch marks if I went out wearing shorts! However, I think bio oil works best on FRESH scars. So if your stretch marks are quite old and already faded a bit then you won't get very good results. Despite this, I keep using bio oil on my stretch marks because it will prevent new stretch marks. Or if any new ones did appear, it will work really well because they will be fresh. I haven't noticed any new stretch marks since using it.