No experience with them, but they look like good bikes, with good reviews. A lot of "custom setup" is definitely marketing fluff, such as tuning the derailleurs and brakes, and making sure the wheels are true. Steerer tube length? I'm fairly certain they are not customizing that, because then they would be making custom frames.
I do not see how they can possibly offer some of the adjustments without actually having you present. There is no measurement for femur length or hand size, for example. Plus it does not take into account the person's flexibility or previous bike experience, other than asking you if you want comfortable or race-like positioning. Lastly, I do not see it spelled out what changes are actually made after you input your measurements. Maybe I am missing something, but when I put a bike into the cart to buy, I do not even see what size frame they would be sending.