I used IRS's Direct Pay for the first time as well. Last year I mailed in checks each quarter, which was easy enough but this direct pay method is easier than envelopes.
I might look into using EFTPS (Electronic Federal Tax Payment System) at some point as it appears that one can setup an account for a nearly one-click payment experience similar to online shopping. Where in comparison, I expect Direct Pay to require me to enter the same information each time the website is accessed since no personal account got created. EFTPS enrollment takes a few days and I got the impression the IRS wanted to steer individual tax payers over to Direct Pay, so I did not bother with it yet.