Please note that the 3D textured mesh is not adequate for measurements as it is not accurate enough. On the other hand, it is a nice representation of the model that can be easily shared and viewed. The quality of the 3D mesh is first and foremost dependent on the quality of the point cloud, so fine-tuning the point cloud parameters is essential. If the point cloud is noisy, the mesh will also be noisy. Make sure that the results from step 1 and the point cloud are optimal before generating the 3D textured mesh.
In order to improve the 3D mesh output, you can fine-tune several parameters in step 2. For instance, you can use the High Resolution settings: yields a high level of detail. This is recommended to maximize the visual aspect of the 3D Textured Mesh. However, computing time and size will increase significantly.
If you go for Custom settings, you can try to use Decimation Criteria - Qualitative - Sensitive. This way the triangles selected have as priority to maintain the original geometry of the 3D Textured Mesh.
Activating the color balancing within the texture can also help improve the result.
For additional information, please read our following article: https://support.pix4d.com/hc/en-us/articles/211083803-How-to-improve-the-3D-Textured-Mesh