I have the same problem... I simply want to show a count/total/max of a numeric field and want to show a green text with " registered". Registered user are a count of an ldap base. Its not possible to select a last value of a field, its not possible to use field placeholders in text panels, all text in a text panel is static, and you cant use the termns(_stats) panel, cause there is only bar, pie or table availible. The stats panel show a number like this, but doesn work and show always "0".
Edit:
I found the solution: you must convert the field to float for the stats panel... eg:
mutate {
convert => [ "registered_users", "float" ]
}