Product review (5 stars): Good as New
Our home is 7.5 years old.  Our dryer is 10 years old.  My wife said that 5 towels took 3.5 hours to dry.  We had heat.  The drum was spinning.  We had air flow to the outside vent, but not very strong.  Google says lint build up is our problem.

We did the following:
1. Disassembled the dryer.  Found a 1/4 coat of lint covering everything on the inside.  Shop vacuumed that mess.
2. Cut out 4 inches of dry wall, adjusted where the vent leaves the wall so it could make a straight shot to the dryer (eliminated 2 elbows)
3. Discarded 4 feet of foil vent hose that was about 40% clogged
4. Used LinEater to clean 26 feet of vent (straight line to the outside).

We duct taped a leaf blower to the house side of the vent and used the LinEater from the outside.  It worked great.  It made a huge mess,
but worked great.

Our first load of towels took 70 minutes to dry.  We are very happy.