There are a number of bonus with the Orion over a DSLR. Here's a few to start with.
1. Thermoelectric cooling = lower dark current
2. Complete capture/focus/primary processing software comes with the camera. DSLR you need secondary software (admittedly you can get most of it free)
3. May well be lighter.
4. Can be saved directly as Fits files
5. 16 bit
DSLR over Orion.
1. Higher Mp
2. Can be used for terrestrial as well as DSO
3. Can be used without external power and laptop connection.
4. Depending on the model - Live view
5. Images can be saved to card and then downloaded to computer. ie you have a backup until you decide to delete them.