Nixie tube clocks are gorgeous but they do cost a lot of money and are not highly customizable. The Elekstube IPS Nixie Tube Clock looks pretty decent but lets you change how its digits are displayed. It comes with WiFi sync. This smart clock has 20 display options. It is USB powered and has a battery backed RTC chip.
The Elekstube IPS Clock supports 12/24 hour formats. The kit comes with LCD glass tubes. It has a plastic base. You can find out more about it here.