Its true. The Invacom quad LNB is the only one we use for getting the best out of the low frequency that 2D uses. And it doesn't seem to last more than 3 years. 2 hot summers on average. They don't break down (unless you have a lightning strike nearby) but they just fade off. Offset LNBs do last longer because of the angle of the dishes they do not have the sun reflecting straight at them.150euros supplied and fitted is about the average(or minimum) to pay a professional installer.I must admit its a good sideline for me.
I do it for a living ,not as a hobby and you do need a good sat meter to align it precisely. Its surprising how many can't get the skew right and can't get the LNB to point to the centre of the dish,and don't make a note of the focal distance before they take off the old one.
Anyway Bigdutch,if you are going to do it yourself ,get an Invacom QDF031 and make a good note of the positioning of the old one.