I actually got the Mitchell years back, when it was payware from MAAM (Mid-Atlantic Air Museum near Baltimore MD.).
Are you talking about the MAAM B-25, because as far as I can tell, it's still payware.
If I remember right, the MAAM design team split up several years ago. The MAAM design team developed a payware B-25, while the group that left MAAM, formed their own design team, and developed the freeware RCS B-25. Both were released around the same time.
Not long after the packages were made available to the public, there was a lot of controversy between the groups over the B-25. MAAM accused RCS of copying their work, especially the textures, and they fought over it for a while. I remember following their arguments in some of the forums.
If I remember right, RCS eventually proved that they didn't copy MAAM's work, and that's as much as I remember

It's been a long time, so my memory is a little hazy
