I use Sonax BSD since 3 years and I'm really impressed by the results, and mostly by the longevity of this "simple" QW.
The BSD gives me a longevity of 2 months approximately. The beading is impressive.
The only drawback is that is not easy to use because the buffing is a little hard mostly when it's hot.
Here my car with only BSD on it
The beading after a heavy rain
I buy this 5L bottle (35€)