It is tough to discuss imports/conversions in a broad sense because the answer really depends on how good you are at problem solving. Lots of people have misconceptions of these aircraft based on limited experience so let me provide some clarification that might give you a better idea of what happens.
First off, there are two labels that I try to use consistently - imports which are aircraft based on FSX mdl files, and conversions which are gltf files native to MSFS. The differences are very important.
Importing Aircraft
MSFS supports mdl file models that are the same format that FSX used, so theoretically you can take an FSX aircraft folder and put it into an MSFS package and it will work. However, MSFS does not treat it 100% the same as FSX so some things tend to break - including transparent objects like cockpit glass. Some models have colors hard-coded instead of using textures, and these are also not supported by MSFS. So in practice, you really need to use ModelConverterX to adjust the mdl file for use with MSFS. This is not necessarily hard as long as you have the patience to learn what the common problems are and how to solve them. Even setting MCX up properly requires tracking down multiple other packages and installing them properly to allow exports - this step is what stops most people before they even start.
Imports also have many limitations - MSFS no longer renders them as reflective so they always appear 100% matte (very ugly). They cannot have interactive click spots in the cockpit. Also many aircraft in FSX relied on 2D gauges that no longer display in MSFS so many panels appear totally blank. Some aircraft might have modeled 3D gauges which might work unless they rely on a code gauge running in the background, which may or may not work in MSFS. Imported aircraft are not supported in VR at all - they will CTD immediately. The final limitation is that these aircraft will likely not be supported in MSFS2024 so they have a limited shelf life.
Back when imported aircraft were a little more worthwhile, a very smart guy wrote the MSFS Legacy Importer, which attempts to automate as much of the process as possible. However, it has not been updated as Asobo has steadily cut back support for imported aircraft and it also cannot solve all of the little issues I mentioned above, like transparent textures. So while it can help you, it almost always still requires some manual adjustment of the files. Many users do not understand how this works so they just crank something through and post a low quality "FSX Port" for download.
Converting Aircraft
A step beyond just importing aircraft is actually converting them from mdl files to the native gltf format. This is pretty advanced stuff; basically you take the mdl file, use MCX to export it in a way that it will open in Blender, then you rework it and use the Asobo exporter tool to export from Blender as a gltf file. Then you need to process the gltf file using the games "Package Builder" which is a whole other complicated process. MCX has the ability to do most of this work for you, but the author of MCX is afraid it will be abused so he has disabled the functionality without a special license that he grants manually to trusted users. This means that in order to convert a plane, you are forced to export it from MCX in a way which strips all animations from the model and then you need to manually rebuild all of the animations within Blender, and also write xml code to control the animations. You also need to reassign all of the materials in the model to their texture files.
However, once you do all of this the end result is a fully native model that is just the same as any other aircraft developed for MSFS. You can do anything that official aircraft can - add click spots, set material properties, attach effects, fly them in VR, etc. The aircraft will take full advantage of the reflections in game too so it will look beautiful! It's just a lot of work to get to that point.
Personally I see no value in imported aircraft any more and I am only working on full conversions, and given the looming MSFS2024 changeover I would not suggest that anyone spend time simply importing a plane.
Happy to answer any more questions!