Most AVCHD camcorders can be used in iMovie without any conversion needed if they are imported directly from the camcorder.
When you hear someone mention that you must convert AVCHD to use in iMovie, it is usually because they removed the files from the camcorder and only removed part of the files and folders. You need all of them to import to iMovie.
However, you should check to see if the camcorder you are choosing will work in iMovie. Here is a list of compatible camcorders.
It takes a while for Apple to test new models.
If the JVC is a new model that is a better version of their old product line, chances are it will work. Companies like JVC are aware that many of their customers use Macs. You really have to be careful of models made before 2008, before the AVCHD standard was popular. To be certain, contact JVC.
The other thing to be aware of is that some manufacturers are offering 60P settings for their cameras. 60P will not import into iMovie without some conversion. It is mainly useful if you need to shoot some very high quality slow motion. But most cameras that shoot 60P can be set to shoot 30P or 30i, which works fine.