Yep been using Fuchs semi synth 10/40 in my 1.9Tdi Leon for 7 years or 142,000 miles. Cant fault it at all. About £20 for this from GSF.
The impreza has covered about 30,000 on Fuchs fully synthethic oil 5/40, about £25 for 5 litees. When I get back from holiday the diff and gearbox oils will be replaced with fuchs stuff.
People are very quick to write castrol off with little or no reason, personally I wouldn't. I sometimes wonder if the same armchair experts have put the wrong Castrol oil into their motor, the Magnatec stuff I have used in the past and cant fault it, there are lots of people get hung up on the wording on the bottle - it says synthetically engineered, as opposed to synthetic oil or semi synthetic oil, is that your mates reasoing for stating that it is crap?
If its for your alfa mate, just put in the stuff that meets the oil spec in your handbook and ensure you change it on schedule, a bit of mechanical by way of allowing the fluids to come up to temprature before you dart her on will extend the old girls life somewhat too.