I've only skimmed over the thread as I'm off to bed, but here's my 2c.
It's not a td42, but still a diesel. My rd28, when I needed new plugs I found out the rd28 plugs were $100 each for the ngk's so I bought cheap nasty ones from a local store at about $20 each. They work, but on a cold morning I have to glow the car 3 times over before cranking otherwise it won't start. And even when it's warm outside I still have to glow it twice before attempting to start it. At least if the engine is at operating temp I only have to glow it once.
So, at least with the rd28 I'm not real keen on the cheap nasty plugs. As that's exactly what they seem to be, cheap and nasty. At least you td42 guys have more options and at better prices.
Matt