I've been using the 4,5. 6mm version for years and finally bought this one due to the proliferation of small Allen screws on brakes and derailleur systems. It's typical Park quality and works great - no surprise there.
After getting Park Tool AWS-1, I realized that I had some hex heads that needed smaller wrench sizes. This tool fit the bill perfectly. So far it has been durable with the jobs I worked on, though I would caution to not overdo it as I expect the smaller hex wrench may strip or break on you if you apply too much torque. A nice addition to my bike toolbox.