Upon the advice of a MBCA member about ten years ago I installed a set of Repco Delux (not Metalmaster) pads. The expectation was for less dust, less squeal, long life, and low rotor wear. The downside is that more pedal effort is required, and I knew that going in.
I installed them at 15K miles and based on wear measurements I've made since then, I expect to begin thinking about replacing them at about 90K miles. I'm currently at 74K.
A bit of idle roughness - an uneven random vibration of variable frequency - appears to be the nature of the 103 engine. I think it's more noticeable on manual transmissions idling in neutral, than an automatic idling in Drive. Modern engines idle at stoichiometric A/F ratio rather than about ten to 20 percent rich as in pre-emission engines, and the leaner idle mixture causes some idle roughness. If you rev the engine up to 1500 to 2000 the roughness goes away. The idle roughness is probably the interaction of low idle speed, valve overlap, and the relatively lean (for idle) mixture. On my car the idle roughness is not present when the car is running open loop during warmup - probably because the mixture is richer, but once warmed up it's there, sometimes worse than other times.
The flex disc that typically deteriorates is at the front, and it will make the driveline feel rubbery. I can recognize it on my manual transmission 2.6 when releasing the clutch and shifting gears, but am not sure how it would manifest on an automatic. For sure you can see if the front flex disc is detereiorated by visually inspecting it for cracks in the rubber. The front flex disc is specifically designed to have flex in torsion to absorb driveline shock. The rear disk is much stiffer and is much less likely to be deteriorated.
I replaced my front flex disk at 60K miles after finding it cracked during my 15K maintenance inspection (I use the MBZ maintenance checklist that the dealer should give you if you have it done there), and it was probably shot before the 50K mile warranty was expired, but I didn't recognize the symptoms until after I replaced it and the "rubber band" feeling in the driveline went away. I expect it will need to be replaced again after 50 to 60K miles. It's designed to flex and the flexing cracks the rubber. Unfortunately it has to be considered as a normal maintenance replacement item, and if you can get 60K miles out of one, you're probably doing okay.