I use Southern Railway's booking system...! Still uses the Mixing Desk style layout, and you can get 25% off 1st ADV fares with SN
I only use the SN website for SN tickets nowadays. I was put off by this in their
FAQs▸ :
Please note, we are unable to guarantee delivery for first class and shall not be obliged to change, cancel, replace or refund a ticket once it has been posted.
This could probably be challenged as I believe they are responsible for the tickets until delivery, but I'm no legal expert. East Coast have issued replacement tickets (via ToD) when some were lost in the post, so I tend to choose them now.