When a Mobile Update action is triggered, it will appear in the Inbox of the Teamdesk app with the title of the action as defined in Setup. This title doesn't show any parameter of the record to update. User only sees what record is being updated when the row in the Inbox is opened.
When a Mobile Alert action is triggered, it will appear in the Alert section. Without the need for "opening", it directly displays parameters of the related record as defined in the alert "Body". However, it doesn't allow User Input columns except custom buttons to be configured.
Now a custom button also allows User Input columns. However, these User Input columns can only be used in a web browser. They don't work in the Mobile app.
Consider the situation when the user carrying the mobile app receives several update requests. If only Mobile Update action is used, he will see several rows in the Inbox, every one looking the same, and he has to open each row to know which records are being updated. With Mobile Alerts, he can read all requests and can choose which one to respond first. But his response is restricted to using custom buttons.
To let the user select the right record to update, I have to do a workaround: use the custom button in the Mobile Alert to trigger a Mobile Update. However this is troublesome as user has to exit the Alert section, open the Inbox, perhaps manually update it, and then open the Mobile Update. I would love to have the User Input columns display directly for use with the click of the custom button without switching back and forth.