This picture depicts an aggressive retrofit of a new construction Dryerbox model 425. The rear wall is a 2x6 non load bearing interior wall. The side wall is a 2x6 exterior wall and falls in an inside corner so the integrity of the wall is maintained. The net equivalent length of this dryer duct run is about 19 feet, well within the code limit at the time of 25 lineal feet.
In this particular case, there are about the same number of turns in the exhaust duct whether done with hard pipe in the wall or flex on the floor. The efficiency is likely improved due to the use of the rigid metal pipe versus the flex hose making all those turns, assuming the owner was venting from the rear of the dryer.