FreeBMD has the General Register Office's indexes (GRO). Yes, you can see the image of the index.
FreeReg works with the parish registers. Totally separate system (they don't use the GRO reference at all). So if you went to a county record office, you would not 'see the same image' as the one on FreeBMD.
If you were NOT the original creator of the WT person, all you would have is the reference (not the certificate). If you were rich, and felt like it, you could order the certificate - but I thought the GRO reference was an acceptable source. It has certainly been acceptable to me, since I am not wealthy.
I really do not like links in these cases. What about all those Ancestry links which someone put in good faith as a source? Now, if you click on them, all you get is a blank Ancestry page, whether or not you have a subscription. So, supposing (in good faith) I put a link to FreeBMD and it loses its funding and disappears? If I had typed the information, at least the viewer would know something.