Mainly in customization and flexibility. You can load drivers (such as driver packs) into MDT and create profiles to deploy to specific models. Granted, that's not as useful for a PC repair business versus a enterprise, but MDT allows for custom scripts, so you can handle drivers in a multitude of ways. You can also have it select from specific applications to install. So for example, if you know they had Chrome as their browser, Thunderbird as their email program and Avast as their Antivirus, you can select those in the walk-through.
I enjoyed MDT at first because it made it easy to deploy images, but lately I've found that just using the bare imageX and some scripting knowledge can provide some powerful, custom automated environments. For example, one of the PEs I've made it completly automated from start to finish which will create a full back-up that contains a text file of the inventory of software installed on the PC (Custom program), a USMT data back-up, an MBR back-up and a Full file-based WIM image. It will then shut the computer down. Eventually, I'll implement some sort of audio or textual notification. There is no framework for doing anything like this with any of the commercial software's available.
It does take quite a bit of time and knowledge to set-up and tweak, so if If you're not ready to commit a good deal of time to it, then the commercial software is a better bet. If you are up for it, then it's a very powerful and you're only limited by your imagination. (That sounded kindy of fruity, but meh)