A huge advantage of McMaster I didn't see enumerated is the 3D models - for nearly every fastener, and for certain other products, you can instantly grab a 3D model and bring it right into your CAD design. As far as I know no one else offers this, definitely not at the scale McMaster's dataset offers. An annoyance of McMaster I didn't see enumerated is how they don't show you the shipping cost until after transaction…
I use McMaster daily and can see the shipping cost in two places when viewing my cart. The lines above the Place Order button on the top right side of the screen has
Merchandise ####.##
Shipping ##.##
Total $####.##
In the same bar below that is tax and directly below that you can click Delivery Method and it also displays the cost for each delivery speed. Maybe if you are set up with an account that is Net-30 this is hidden, but it certainly shows up for me when set to process the transaction by credit card.