Don't believe the hype: corrugated flexible aluminum ducts aren't as good as old fashioned 4" galvanized ducts. Every corrugation serves as a lint trap, and eventually the whole thing becomes blocked with lint. Plus, after seven years it becomes too difficult to put the duct back on after you've pulled it off. (Never use plastic flexible duct. It will burn your house down without a second thought. And you should really clean out the ducts every couple of years.)
The dryer works a lot better now, drying clothes in much less time than it did before. Which means I'm using less electricity and natural gas, a definite plus when the price of natural gas is expected to go up 40 - 70% this winter compared to last winter.
I have always thought that there should be more midget plumbers. (Picture a Very Large Man working on a sink with his head, arms, and shoulders jammed into the cabinet under the sink to understand why.) Now I've decided that people without legs who also weigh about 60 pounds would be perfectly suited to work on clothes dryer maintenance. Most laundry rooms are not set up to hold a washer, a dryer, and me squeezed between them, trying to tighten hose clamps and avoid dropping my tin snips on the gas line.