I've bought a bunch of stuff from Marco, usually it's very high quality.
The only item I have bought from them that I was disappointed in was their "Nuts/Bolts/Washers" assortment. They advertised it as containing the most commonly used parts, and since I always seemed to be missing some part it seemed like this would be a good idea.
Unfortunately, other than using a couple of the washers (of which there was only 1 size), none of the other parts even seem to be on any of my machines. Not that it was a big deal, but it really seemed like "parts no one uses" rather than "parts everyone needs".