A slight variant will be the 4-3-3 Flat, and you must use this if you want to share the attacking and defensive responsibilities amongst your midfield 3. You can go in a bit of 'no-man' s-land' in between the attack and defense having said that, so appear for personnel with higher function prices. Maurizio Sarri has used this technique brilliantly with Napoli and now Chelsea. Jorginho has been essential, with all the Italian sitting deep and hunting to play the ball forward promptly towards the attacking players ahead of him, something Eden Hazard has enjoyed this season. 

FIFA Expert's recommended work rates:
Right Back – Medium Attacking / High Defensive
Left Back – Medium Attacking / High Defensive
Right CB – Low Attacking / High Defensive
Left CB – Low Attacking / High Defensive
Right CM – High Attacking / High Defensive
Left CM – High Attacking / High Defensive
Central CM – Low Attacking / High Defensive
Right Forward – High Attacking / Low Defensive
Left Forward – High Attacking / Low Defensive
Striker - High Attacking / Low Defensive

Strengths: The 4-3-3 is one of the most famous formations, and this is understandable for a few reasons. It allows you to mix up your passing style with short passing in the middle as well as the option to hit the wings with more extended passing. The two wingers provide plenty of widths so crossing opportunities will be plentiful and a big reason for its popularity - it's an excellent formation for counter-attacking. 

Weaknesses: The main weakness is that the lone ST can be left exposed when going forward, especially if your wingers lack pace or have medium/high defensive work rates. Another is related to the midfield 3, if your CM's have high attacking & low defensive work rates they leave your back 4 exposed, particularly if your opponent recognizes this and is playing a formation such as the FIFA Formations 4-2-2-2 or 4-3-2-1. Representing, as with the 4-3-2-1, at least one more defensive-minded midfielder is advisable. 

Key player/position: 3 CM. In this set-up, it is vital that the three midfielders are all comfortable on the ball but also have a bit of steel about them to win the ball back. If you have three attacking CM's, then the likelihood of you getting overrun at the back becomes a high possibility. Choose these three players wisely and build your team around them.

Most suited style of play: Wide areas are a crucial part of the success criteria for this formation. Again, focus game initially through the CM areas before distributing to Wider players. Also suits a counter-attacking style of play.