I see maybe 10+ failed DMFs here a year. It is pretty common. On the TDIs, the frictions rarely ever totally wear out. Almost always the reason I am taking the transmission out is because the DMF is coming apart (or already came apart). DMFs were failing before the TDIs even got them, way back in the '90s, on 1.8t Audi A4s. So it isn't like this is some "new" revelation.
Used to be, the one piece flywheel conversions became popular because the DMF setups were so nuts expensive. At one time, it was literally double the cost.
Now, the aftermarket offers Sachs and Luk DMF/clutch setups at a reasonable price, and they are often within spitting distance of the popular one piece conversions of a reputable brand.
The DMF by design works great. Smooth engine operation, smooth engagement, and the actual clamping force is generally fine (again, the frictions rarely wear out). But when they break, and they do, it can be pretty catastrophic up to ruining the transmission. That is rare, and in most cases those DMFs were driven bad for a long time and were simply ignored.
The one piece flywheel won't break. Ever. It can't. It is a solid chunk of machined steel, versus about 20 pieces ("dual mass" is a bit of a misnomer, as there are LOTS of little springs and gears in them, too). The downside is that even with a conventional spring tensioned disk (DMFs have solid disks), they generally are not quite as smooth engaging. But, just to point out, converting an ALH to the old style is not going to hurt anything. The earlier 1Z/AHU engines had one piece flywheels too, from the factory. As do most of the base 2.0L gas engines. The conversion kits are just using some slightly modified but basically off the shelf parts used in other VAG products to make everything work. The early versions that were popular were just off the shelf Sachs parts used with G60 (supercharged Corrado) and early VR6 engines. Now, Sachs, Valeo, and others make conversion kits and are sold as such.
So, the choice is really up to you. The original lasted 215k miles. Chances are it was a Sachs unit, and a replacement Sachs DMF setup will last just as long. There are also Luk units available, and they may be less costly, and may be pretty close to a popular conversion like Valeo (what we usually sell here).
I have installed a LOT (hundreds) of the conversion kits. I have only ever had three people not like them, two of which I gladly changed out to a new DMF setup for whatever the extra cost of the parts was. The third, when faced with spending more money, decided it "wasn't that bad". Sometimes cheapness wins. But in the end, at least he'll know his one piece flywheel won't break. Plus, in 1/4 million+ miles, if it actually needs a clutch job due to normal wear, you can just buy the clutch kit with no flywheel, and it will be a pretty inexpensive bill.
