Mahle do two ranges. They do a 4032 alloy range, and a 2816. The 4032 are like your typical forged piston. They have a higher silicon content and so expand less than the likes of Wiseco/some JE/ etc This means that you can safely run almost OEM piston clearances. This gives very good piston and ring life as the pistons remain straighter in the bores, and very little oil use.
The second point of the 4032 is they include a whole load of 'features' that you have to pay as extra on almost all others. They have a low friction Grafal skirt coatings, the piston is Phosphate-coated (this is what gives them the grey look - not shiny alloy), friction relieved ring lands, high quality and very strong wrist pin clips, (not spiro-locks) low friction, race piston rings, (these are tough, you realise how so when you gap them). The other thing is they are very tight on tolerances. You will find they often don't need balancing, and that the machining of each pistons are such that you don't even need to match the engine boring to suit. Basically they are a very good piston upto about 450-500hp, the only reason you wouldn't want to push the 4032s further, is that due to their low expansion they are compared to the 2816 pistons slightly more brittle. (but no weaker than say other competing products advertised as taking much more power). It just means that if you ever experience det or very high rpm etc at very high power you may break the ring lands where as the 2816 most probably wont. The final nail in the coffin to competing products is they are cheaper. Its a Win-Win. More here:
http://www.us.mahle.com/MAHLE_North_America/en/Motorsports/Power-Pak-Pistons
The 2816 pistons are full race pistons. IMHO better (sorry Danny) than anything CP/JE etc do. This range are proven on 4cyl 2.0 engines to take over 1200hp, currently hold the fastest 4cyl 1/4 mile Subaru in Europe, and will withstand far more power than anything anyone here will do. They have all the same features of the 4032, just require slightly larger bore clearances (same as you would on other pistons anyway). These are even more precisely matched and hand de-burred. They are about 15% more expensive than the 4032, but still not expensive.
That, and the fact I can get them easily & they have worked very well for me, and the machine shop I use has an enormous amount of experience with them (they do most of the machining for many of the Tuning places in the SE) means for me its a complete no-brainer!!
FYI prices for SR20 4032s are about £500 ish, and 2816 are around £580.