I think the complaints that you mention might have a lot to do with perception.
Someone that buys a cheap pump (I didn't say bad) is less likely to complain when it fails because it did not let them down. It met the user's expectations. They feel as though they got what they paid for.
Someone that buys an expensive pump (I didn't say good) is more likely to complain. When it falls because it did let them down. It did not meet the user's expectations. They feel as though they did not get what they paid for.
There are plenty of people on both sides with the opposite experiences where everything is great.
That being said. Let's get real. Most of those happy people where everything is great have Tunze pumps.