I'm working on an import/transition from RM7 to FH7. Most things here apply to RM8/9 as well.
All in all, it is amazing how well my RM data transferred with the FH7 direct import. More importantly, FH7 provides a framework where the imported RM data can be utilized as it is. However, that does not mean your RM data and the RM way of doing things complies with "best practices" for FH7. My impression is if someone tries to simply continue using their RM data in RM ways in FH7, it will be very much like swimming against the current. RM and FH7 are conceptually different. As the old carpenter says, "its works best if you use the right end of the hammer."
Here are a few issues you will encounter with your RM data import to FH7:
If you have exploited features of RM's Fact sentence structure, FH7 does not translate everything. The FH7 sentence building tools are extremely powerful but with that comes a little more complexity. I did quite a bit with RM sentences and so far I have been able to translate and even enhance my fact sentences in FH7 but it took some time and there is a learning curve.
- The RootsMagic "switches" structures don't translate well but there are FH equivalents.
- References to data in the RM "Desc" field may need attention. Since RM does not allow the note field in sentences, RM users have shoehorned all kinds of things into Desc. Generally [Desc] is imported as {cause} in FH7. {value} may be substituted if {cause} doesn't fit your fact definition. Usually, the needed adjustments are not difficult and the ability to include {note} and {inline-note} in FH sentences helps a great deal. Its what RM users have wanted to do for a long time.
- The Rootsmagic [Husband], [Wife], and [Spouse] values do not translate but there are FH equivalents available.
- [Place] and [PlaceDetails] translate to {place} and {address}, but FH handles punctuation and spacing differently, so adjustments may be needed.
- References to people in roles like [Bridesmaid] do not translate, but they can usually be replaced with the FH {role=Bridesmaid}.
- If you refer to a person's age with [Person:Age] or [ThisPerson:Age], RM calculates the age of the person using the date of the fact and a birth date, if available. This RM reference imports as {age}, but that refers to the age field of the fact. Since RM does not have age fields for facts, this will never produce a value. There is a function in FH that will calculate the person's age as RM does that will produce the desired result.
Some RM features that don't have a FH7 equivalent get transferred as "metafields." For example in Source fields, RM allows a full version and an abbreviated version of the data to appear in the same field separated by "||". The abbreviated portion of these fields is written to the citation note as a metafield. These metafield values can be referenced with the GetLabelledText function. Another example is RM WebTags become metafields in the FH citation note field.
RM Alternate Name facts have associated dates and source citations. If you import alternate names as facts, the sources will not be attached to the imported FH fact. If you also import the alternate names as secondary names, the citations will be attached there. If you import alternate names as facts the date will appear in the imported fact, but there is no provision for a date for an FH secondary name. Having a date associated with a name is not part of the GEDCOM standard.
Almost all of my sources are based on custom RM source templates. They all imported and with the exceptions mentioned here, they imported very well and work in FH7 the way they work in RootsMagic.
Some source template footnote/bibliography formatting does not come across. In this case there are some issues for which I have not found an equivalent. 1) Citation fields cannot appear in bibliographies. (In FH's defense, they seldom should!) 2) The [Place:REVERSE] RM construct returns the place parts reversed, separated by periods (full stops). This is EE standard for Bibliography entries where the place is the leading element. There is a FH7 function that reverses place values, but it returns them separated by commas.
That has been my experience thus far. I'm sure there will be other things not yet discovered, but all in all, the import was extremely complete and I'm very impressed with how robust the FH7 options are for taking care of differences.
How far I want to go converting my data and workflows to better suit FH7 is the more difficult question and it comes with more involved answers. I have a lot more work to do in this regard.