Trimming a Beef Tenderloin is not really that complicated. Some may find it a little gross, but the savings you get is well worth the effort. Once you have done it a few times, you will get more and more proficient at doing it.
The first thing is to have a sharp knife. This will make it much easier to cleanly cut away only the pieces that you want to remove. Second, have a big cutting board to work on, ideally with a little channel along the edges to catch the blood that drips off. Third, the cryovac package that it comes in over the sink, because there is blood in there that will be all over the floor and counter if you are not careful. Once you have opened it and left most of the blood in the sink, move the tenderloin to the cutting board.
When you have finished all the trimming separate the filet into three potions as shown here.
The bottom right portion is the prettiest and is what I will use for a nice Chateaubriand. It is also great for slicing into filet mignon steaks. The top right can also be used for the same. It tastes the same, but it is just not as pretty. The other piece is too small around for steaks, so I plan to use that sliced for a beef and broccoli stir fry dish later.