I have a couple of pairs of DMs.
One pair (cherry red knee highs) I've had for maybe 11 years. They are a bit scuffed now and have needed 2 zip replacements but they are still fully functional and still waterproof.
For info, DM have paid for both zip replacements, they don't do them themselves, I took them to store the first time and they said to get the zip replaced and bring in the receipts and they'll reimburse. Which they did, no problem.
They offered to replace the boot for free, but I wasn't willing to spend 3 months wearing new ones in.
I've never bought another brand of boot that compares, no idea how they can get it so right and everywhere else can't.