The best way to clean a dryer vent

I posted this questions 6 months ago..

Why does it take my dryer 3 hours to dry a load of clothes?

I checked the cycling thermostat and thermal fuse. They are operational. I have seen different ways professionals clean dryer vent ductwork. Coit services used a portable compressor to blow air into the vent the push out lint. There was a good amount that came out.
But I have seen another method where they used a rod with rotating brush that push out lint. I am thinking of hiring someone to do it this way. Is this a better way than what Coit did?

My tenant last said the timning of drying has improved form 3 hours down to 2 hours. I'm not sure how long of dryer vent ductwork she had at her previous residence. I can understand if she had a dryer close to an exterior wall with a 1 foot of dryer vent. I may have to ask her that. Everything is relative. If there is a longer run of duct it should take longer to dry no? Any feedback would be appreciated. We really want to take care of this tenant because they are nice people.