Having used both extensively, Geizhals doesn't hold a candle to McMaster. McMaster is, bar none, the single best e commerce website I've ever used (if you already know what you're looking for, and definitely still top shelf if you don't).
But McMaster and eg Amazon are optimizing for different things. McMaster knows its clientele isn't going shopping, they're solving problems. As such, McMaster focuses on helping your solve your problem and get back to work. Amazon, on the other hand, is focused on just selling you "as much 'anything' as possible" and wants you to spend as much time there as possible in the hopes that you'll stumble on an impulse buy.
But McMaster and eg Amazon are optimizing for different things. McMaster knows its clientele isn't going shopping, they're solving problems. As such, McMaster focuses on helping your solve your problem and get back to work. Amazon, on the other hand, is focused on just selling you "as much 'anything' as possible" and wants you to spend as much time there as possible in the hopes that you'll stumble on an impulse buy.