Here is a little experiment you can do to give you an idea of the improvement these make.
Take off your door speaker cover to allow access to your front speaker. Then remove the speaker but leave it connected. With the speaker in your hand out of the door turn on your radio. Now as the music plays move the speaker in the door and then out. It is amazing the difference an inclosure will make even if it is as poorly designed as your doors.
These will make a huge improvement for people that have speakers in the rear without any inclosure of any sort.