The course are nearly the same, and the requirements for instructor are nearly the same.I did the SDI Solo course; my instructor is a private TDI Tech instructor. I went that way, as opposed to a PADI class from a local shop.
I am not an SDI solo instructor, but according to a website I just checked, here the requirements to be a SDI instructor:
- 21 years old
- OWSI or higher certification with a minimum of 1 year teaching experience and 50 certifications across a range of courses
- Solo Diver (Another site that advertises itself as official SDI/TDI does not include this requirement)
- Be a Teaching status PADI Open Water Scuba Instructor
- Have certified at least 25 divers
- Be a PADI Self-Reliant Diver or PADI TecRec Diver, or have a qualifying certification from another training organization
- Have logged at least 20 self-reliant dives (dives using redundant equipment and following techniques of self-reliance)