From what I can remember, I believe they are effective. Harry has a piece at https://www.vitamindwiki.com/tiki-index.php?page_id=2136. Up at the top he states “and may not be kept up to date (should be able to do so, but it does not seem to work)”. I am not sure why he made the statement “does not seem to work”. (I will let you read it.)
You have to make sure it is D3 and not D2.
I found two comments out there in which people specifically stated that it did raise their levels. So from what I remember it works but is expensive unless the price has dropped with more manufacturers. Nordic Naturals has one and there is Vita shine and I think some others.