If you are comfortable with your current set up as far as reliability and all that, and all you want is a pin code panel, have you considered using the iris keypad combined with some of the community code that can add a delay?
Again, it doesn’t run locally and it can’t improve the existing reliability issues of the SmartThings platform (two areas where the ADT model does have some improvements), but it’s a keypad with a delay if that’s really all you need. 
https://www.amazon.com/Iris-Smart-Home-Management-3405-L1/dp/B01GCKAFX8