I have been using TreasuryDirect for a year and love it.
I closed out my Treasury Direct account couple of years back. Website was clunky, logging in with digital keyboard was hassle for me. It locks out after couple of attempts, then dealing with customer service was nightmare for me.
Converted Paper bonds to digital, it took forever to show up. I realized if something happen to me, my wife who is computer illiterate won't deal with all the issues. Also if i remember correctly, it won't mail out 1099's. May be things have improved recently, but I won't go back. Rather pay expense ratio with funds or ETF's.