auto visualizer does not always work.
take the example of code:

#include <stdlib.h>
#include <iostream>

struct MyType
{
  int _value_;
};

void test1(MyType mt) {
  std::cout << mt._value_ << std::endl;
}

void test2(const MyType mt) {
  std::cout << mt._value_ << std::endl;
}

void test3(const MyType &mt) {
  std::cout << mt._value_ << std::endl;
}

void test4(const MyType *mt) {
  std::cout << mt->_value_ << std::endl;
}
int main()
{
  MyType mt{10};
  test1(mt);
  test2(mt);
  test3(mt);
  test4(&mt);
  system("pause");
  return 0;
}

and create a natvis file:

<?xml version="1.0" encoding="utf-8"?>
<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
  <Type Name="MyType">
    <DisplayString>[{_value_}]</DisplayString>
    <Expand>
      <Item Name="Value">_value_</Item>
    </Expand>
  </Type>
</AutoVisualizer>

if you create a project that Win32 Visual C++

if the project is to create MinGW/Cygwin VisualGDB