Fallguy- I'm guessing that you just don't like how the FK1000P looks on that particular vehicle (otherwise, why not just use it all by itself). I wouldn't expect any problems with any of the products you mentioned, I'd just go by which you'd rather have on there- 845 for an overall decent product (OK on trim, easy to do); M21 for durability and its look (if you like it); OCW if you just want to do it quick/easy and don't mind redoing all the time.
Regulars here probaly *know* what I'd do, but I'm kinda a FK1000P fanatic ^_^