I've tried several different 1" square shoulder end mills. I use them mostly in carbon and stainless steels. I would encourage you to consider a 3 flute. I used a four flute Seco Turbo mill for awhile, but the insert pockets wore out quickly. Later, I was talking to an Ultra-dex factory rep, trying to buy another 1" 4 flute, and he told me that they had discontinued the 4 flute version. The problem with four flutes in a 1" end mill is that they can't put enough meat behind the insert in order to absorb the shock, so the pockets wore out too quickly.
I switched to a 3 flute Seco and had much better insert and tool holder body life.
Based on in-house testing we had the best tool life and metal removal rates using Dapra cutters. (Which is what we currently use.) Seco Turbo Mill, Iscar Helimill, and Mitsubishi (APX series IIRC) were all pretty close to each other with both MRR and tool life. The standard APKT insters (we tried Koraloy and ZCC) were not even close to the same tool life or MRR as the others.
At the time of our testing ( a few years ago), Mitsubishi was the least expensive followed by Dapra then Iscar. Seco was much more expensive. Because of the better tool life the Dapra end mill had the lowest cost per cubic inch of metal removed.