Thanks for the info everyone
The pin holes are only visible when directly over the sun - they are not visible just by holding it up to even bright lighting, so I guess it should be ok.
I think I might keep it, (its the proper Celestron one that mounts directly on the end of the C8) since it was the last one in the shop.
The view was interesting, but kind of boring - only very faint detail and no sun spots
Guess I will have to wait until some appear.