The databases that form the Family Search collection of Irish records has gone live today on Ancestry.
This includes the Civil Registration Indexes as follows:
Births and deaths for the entire island 1864 to 1921
Non-Catholic marriages for the entire island 1845-1921
Catholic marriages for the entire island 1864-1921
Births, marriages and deaths for the 26 counties of the Republic 1922-1958.
In addition, Roman Catholic parish register entries from various sources (the old IGI as well as incomplete data culled from some parish registers).
The benefit of the Ancestry option is that the marriage searched returns can be additionally searched to find all the names that appear on that page of the register volume. That's a real improvement. And the search facility just feels better (never have liked the LDS search). But, of course, it doesn't come free.
You pays your money and you makes your choice.