I think the words 'mail order tune' usually mean plug and play. This isn't the concept many professional tuners adhere to, especially in this day and age, although I'm sure it's the concept that was used back in the 90's extensively....and it's still a matter of you get what you pay for.
Rather than purchasing a mail order tune, many professional tuners sell a service. The service requires the customer to email their stock tune, the tuner to modify it and the customer to install that modified tune. In many cases, you'll get a 90% fit on the first pass, especially with minimal mods, but that last 10% will need fine tuning with data logging and tune revisions.
In any case, even with a 'traditional mail order tune' surely if it's written specifically for your truck wouldn't it be better than a generic off the shelf tuner that everyone has used for years that needs to cover all mods, all altitudes, all diving purposes and conditions?
Cheers
Cindy