Open cart custom fields allow you to add 9 types of fields. You can also display new fields for specific products, categories, customer roles, cart total, and cart items. You can customize, edit and disable the default checkout fields as well. Data manage easy from back end. you can easily sort-out according to the fields. Multiple layouts with mandatory and optional fields.Make your store more well structured  with opencart custom fields extensions. 

https://opencart.extendons.com/octestimonialsplus/admin/
for checkout manager Demo:
user: checkout
pass: checkout