This seems like something that is easy for me to do myself. I deposit a check in my bank account and either manually or automatically move some percentage of the money to a separate savings account. I guess I don't see what value this adds?
There are a handful of people who are in the same boat you are and handle their taxes on their own with no problem. That said, for the vast majority of us, setting money aside and not touching it is really (like, REALLY) hard. Painless gets cash from freelance gigs out of sight and out of mind before you feel like it's money you should dip into. Beyond that, the automation of a process you'd have to do manually otherwise is something we think everyone can get behind whether you have a process in place currently or not.