I agree with most that the competitor here is McMaster-Carr. The collateral damage could be places like Lowes/Home Depot etc (brick and mortar supply stores) but agree with most here that SmallParts (which this was created out of) didn't have quite the execution that McMaster-Carr does.

The other bit is there is the whole interaction model. In the fabricator world they seem to get an account with one of these companies, order various bits all month long and then get a roll up once a month or so on their purchases. That doesn't seem to be an Amazon compatible model yet.

It will be interesting to see how it works out.