Anh - it seems I have stumbled across a few issues with frontend submission that are causing me issues. In general, forms that use the special field type Group and also Tabs that are using the LEFT layout option - these elements cannot be displayed using the MB Beaver Themer module, and also, there seems to be an issue submitting data and then associating it with a CPT. You are working on these issues and I know you will create a solution for each when you can.
However, while you sort through these issues, I need a work-around pretty quickly. So I'm asking about using a third-party form plugin. I want to use MB to create the CPT and custom field meta, but then use another form plugin to hook into the custom fields so I can create visually complex forms and also add/edit data using custom form fields without any issues.
I know that Gravity Forms has its own method for storing form submissions. But can you suggest a different form plugin that works better with the native WordPress construct and MB?
We have resolved the problem of storing custom fields 🙂 Only the layout issue left.
Regarding the 3rd party form, I have experience with Gravity Forms the most, and it works really well for all the situations I had in the past. So it's my obvious recommendation. WPForms and Ninja Forms are also popular, but I don't like their UI in the back end. Ninja Forms used to have a nice UI that blended well with WordPress, but it changed :(.