It seems to be a very unreliable resource, on top of being quite expensive
That just about sums them up.
You have to remember the sources of data. The LDS Pilot site is transcribing the official state BMD records, and should therefore be full, but the caveat is that records are no earlier than 1845 for Protestants, and later for Catholics. But if you are searching fior the period they cover, then the Mormon site will inevitably have the record
The other lot IFHF are a bit like Starbuck franchises, it just depends on the local outlet as to what they have to offer.
The problem is that it is practicably impossible to know what they have. Neither Catholic nor Protestant churches are obliged to give them any records - it just depends on local clergy.
Each IFHF county site shows at the top of their main page their sources and if you click that you can see what they claim to have. But that list is not necessarily either complete or correct.
The Irish National Library (for Catholic) and National Archives(for Protestant) church records has a fullish set of fiches from parishes, that is better than the IFHF records. Bear in mind also that IFHF have transcribed onto cards and that is what you get from them, not a copy of the original as with say Scotland's People. But again some records are still with local clergy and not available in Dublin.
So bottom line is if you cannot get to Dublin to check yourself, you are stuck with LDS site for state records, and IFHF for earlier (unless you can find a transcription elsewhere)
Ireland is very badly served by IFHF sites and offices. I assume some politician made a bad decision to set the thing up in the first place and the thing cannot be reversed. The IFHF are unable to comprehend that genealogy is all about trawling records to find leads, and that few people know exactly when and where g-grandfather was born to get the right certificate.