I used to be really into car stereos a few years back, so my perspective may be out of date, but what I remember is that they are both very comparable brands in the car stereo market. Alpine was very popular in the states and if I remember correctly, they were featured in Lamborghini vehicles where as Blaupunkt was featured in Ferrari's (factory stereo manufacturers).
Now I can not speak for the current aftermarket offerings or quality of either company or on this specific head unit, but personal preferences led me to Pioneer car audio and then SONY for head units. I put Pioneer head units in my first 3 cars (Ford Probe, Jeep Wrangler x2) and did not have a single complaint, they were in the one hundred to few hundred dollar range. Then SONY released a single din unit that had a sweet LED screen but no internal amp. All said and done, that ended up being a bigger money-sink than I hoped for; reaching well past a thousand. And then that was all traded in with the Subaru. Now, since the BMW and MINI are not friendly to aftermarket stereos I have left the head units well alone and kind of faded away from that whole scene.
