Product review (5 stars): the mildew smell became pretty noticeable. I don't think the brush the duct ...
Picked up a couple of these sets because I have a 30' long dryer vent run and the duct cleaning company I paid couldn't take care of obvious mildew that had developed in the vent. Initially, there was a really nasty smell (like something crawled up there and died) - after the duct cleaner came out the first time he didn't find anything but got a lot of lint out and sprayed bleach inside. While the really awful smell was now mostly gone, not long after, the mildew smell became pretty noticeable. I don't think the brush the duct cleaning company had was long enough to reach in to get to the trouble spots. He was running a blower and got a lot of lint out but the smell persisted even after he came out a second time and sprayed bleach into the duct with a compressed air gun.

At this point I decided to DIY it, and I'm glad I did. I initially didn't have a keyless chuck drill around when I got the Deflecto kits so I tried by hand - I put 12' (one kit) down the vent from the laundry room and sure enough as I was pulling it back up the rods were wet with that rank mildew smell. I think this was a result of lint that had gotten wet and stuck to the walls of the duct like paper mache. I finally obtained a drill from an old coworker and went to work. Setting the clutch on 4 (as was recommended by another reviewer) was perfect at least on a Hitachi cordless drill set. I first went in on low gear and from both the laundry room and from the outside exhaust. Probably made 2-3 passes in total then ran an electric 165mph leaf blower duct-taped around the vent from the laundry room. I could still detect the smell so I went in on high gear and several more passes, again using the leaf blower to blow out excess. More stuff came out but the smell was less noticeable. I went ahead and poured about 1/2c-1c of baking soda into the vent and used the leaf blower to blow it through and then hooked the dryer back up. It's been about a week now and there's barely a trace of that mildew smell. I think the combination of going through with the Deflecto kit again and then letting the leaf blower push air and dry out the duct really helped by leaps and bounds.

A few other things to note:
- There are three 90 (or close to 90) degree bends in the 30ft duct run, which runs underground. It was a bit tricky getting around the first bend the first time but after that it was pretty easy.
- I didn't tape the rods together as recommended - I felt this would be too tedious since I was screwing/unscrewing each section as I was pushing it in or pulling it out.
- Go slow but don't hold back on the high speed gear setting (if you have one) - just make sure to set the clutch low and ALWAYS drill/turn clockwise so as to not undo any rods
- I was scared I'd have issues like a couple others who took pictures, of their rods getting twisted up really badly. This didn't happen - I can only imagine that happening if you go in too aggressively and too fast without using the clutch and trying to drill in a super long section of rod (rather than going piece by piece)
- I thought with two kits I would see the brush head pop out of the exhaust but I was still 5-6' short
- I bought a 30' snake cam (by Bluefire) that I was able to use to check on the condition of the vent before/after/in-between each cleaning. This was SUPER useful - I had to attach a small LED flashlight to make it more useful for visibility. But after the duct cleaner did his thing the first time, there were MAGGOTS crawling around inside the duct!

I would highly recommend this for anyone looking to clean out their dryer vents. I should have just bought these from the get-go instead of hiring someone. Now I know... It's also cheaper buying two of these versus the Linteater kit, which runs $28 or so. The difference is that you don't get all the extras/accessories that the Linteater comes with - those extras *may* be useful especially if your ducts are really clogged up. But instead of the extras/accessories you get the extra length with 2 kits. In my case, all I needed was the brush and rods (and extra length).