This is a tough question and am not sure it can even be answered. You would have to look up your parish in both FS and Archion (the search is free) and see if records are in both or either. That would save you from having to purchase a subscription.

That's true, but one big advantage of seeing the original record in Archion is that you might pick up lots of other information that the standard FamilySearch or Ancestry database does not include. Things like the names of witnesses (could be other family members); other births in the same family (by looking through other pages of that parish book); occupations; comments by the pastor (I had one saying the child died when he was being carried by his sister and they were frightened by a chimney sweep, which caused the child to have convulsions!); and more.

The downside is, none of the records are indexed or searchable, though some parishes have compiled handwritten indexes by first letter of last name and year. Once I found the births for an entire family all on one page of the parish index, so I could go find each child's record. Also, you must learn how to read German script, understand some German, and enjoy puzzling out what a record says. This group can help with that.

In my opinion, Archion is worth the money! But yes, first see if parishes in your region are available on Archion. Then have some concrete goals before you buy a subscription, like an ancestor's name and approximate date of an event. You can buy a short-term subscription and just do your best to make the most of the time.