GRONI indexes are great for being able to get access to the images very cost effectively ... as long as you can find the entry in the indexes in the first place. Irish civil registration indexes have been available on Familysearch for free and several of the subscription sites like ancestry for a while but several times I could not find a record on GRONI that was clearly indexed on these other sources before the time limitations of the GRONI data online i.e. births over 100 years ago, marriages over 75 years ago and deaths over 50 years ago.
My main gripe, like many others, is how clunky and tedious the GRONI search screens are. Having to keep calculating 5 year windows is extremely annoying, especially the "helpful" messages that keep popping up to tell you that you can't count! Why are we limited to 5 year windows and why can't they be automatically calculated from a start year? Oh, and another thing, you cannot search just 1 year on GRONI i.e. you cannot make the start year and end year the same - why not?
Despite the fact that our ancestors were fond of middle names, don't expect to find any in the GRONI results pages to help you narrow down your search. However, you will find fuller names in the familysearch or ancestry indexes so have another tab open and cross-reference against the results returned from a similar search there. Having complained about GRONI, it's only fair to point out that for births, their results pages and the search facility do have mother's maiden name for all years available which is brilliant, helping you to find candidates for ancestors' siblings.
On the subject of names though, no wildcards are allowed and I'm not impressed with the "variants" option for names. For example, the client research I've just completed involved several names prefaced Mc but what you often find in the transcribed indexes is M', which the GRONI site failed to find.
It would be interesting to know what the rationale was for the clunky site design and whether there is any chance of being able to influence improvements. In the meantime, keep working those different sources together and hopefully you will find what you seek.