The company was founded in germany - they used to do a lot of "high end" oem installs for porsche, bmw etc. IIRC Blaupunkt means Blue Point in German.They were a long time subsidiary of the bosch group.
I used their HU's for over 10 yrs and was never disappointed. That consisted of 3 or 4 different units, all among Blau's lower end.
I recently replaced an $80 Blau with a $200 eclipse and wasn't blown away by any means.
Their aftermarket stuff is generally average. It's definitely not Pyle/Pyramid/Boss garbage, but it's not Alpine or JL either.
They made some noise a few years ago when they released their PA line of amps using class T topology. They were VERY small and efficient, but eventually got a rep as not being very reliable. That's about the last time they were "popular".
In 09 they were sold by Bosch and I haven't seen much out of them recently.
I would expect Blau's worst stuff is better than Boss's best.