Concept art for the suit states that it is still in the prototype stage of development and is thus unstable, potentially being dangerous to the user. It is not clear if this is canonical in the final game.
According to the development team, they wanted each combat rig to look like it could belong in the single player campaign, even though they were designed for multiplayer. However, they realised that the FTL rig was much more sci-fi than any other design because it was composed of purely prototype technology, which meant there was nothing else in the game that really resembled it. Thus after they had put the FTL in multiplayer, they went back to the single player campaign and added several in as SetDef soldiers to ensure the suit would not look completely out of place in multiplayer.