First of all, congrats to the OP for the accomplishment.
Next, in relation to the following
<snip>PADI Master Divers equivalence more closely to NAUI Advanced Divers. NAUI Master Divers are expected to be at the skill and knowledge level of NAUI Instructors. Very few PADI Master Divers (or for that matter NAUI Advanced divers) are prepared to attempt a NAUI Master Diver course, it's just not the same thing.
I agree that the NAUI MSD cert and the PADI MSD cert are very different, but the above is an oversimplification that I believe gives a false impression. I base my objection partly on personal experience and partly on NAUI's published course requirements. I realize that NAUI instructors are permitted and even encouraged to beef up the curriculum and add dives to the minimums published by NAUI, but they are not compelled to do so. The effect of this is that a NAUI course offered by a particular instructor may not actually follow the same curriculum as the "same" course given by a different instructor. Therefore, the only real way to compare PADI MSD and NAUI MSD certs is to look at what each requires at minimum, not at what each "might" include when under the direction of a superlative instructor.
I earned the NAUI Advanced cert, and it is nothing at all like the PADI MSD. In fact, it's very similar to the PADI Advanced cert. So the assertion that PADI MSD is equivalent to NAUI Advanced is quite simply untrue.
In terms of comparing the NAUI Master Diver cert and the PADI MSD cert, it's not clear cut. NAUI's cert appears to be more demanding than the PADI cert in some ways and less in others, based on the published course requirements available online from the NAUI website. If a current NAUI instructor can demonstrate that the published information is incomplete, perhaps we can make a more informed comparison.
- The overt theoretical knowledge required of the NAUI MSD cert is more explicit than for the PADI MSD cert, which requires no written tests beyond those required for particular specialties and for Rescue Diver.
- For NAUI, some Rescue Diver information is folded in to the course with classwork and a single required dive, whereas for PADI it's a separate required course which takes several days to complete and includes a written test. (NAUI does have a Rescue cert, but it's a specialty and is not a listed requirement for the MSD program.)
- The PADI program requires CPR + First Aid training since that in itself is a pre-req for Rescue; no such requirement is listed for the NAUI cert.
- The NAUI cert is more strict with the obligatory dive skills, which include additional work on nav and low viz diving plus search and recovery and introduction to deco diving, as well as the emergency/rescue dive. The PADI cert allows the divers to select which specialties will meet their particular interest, even if these specialties are not specifically designed to enhance dive skills such as navigation.
- The NAUI cert is less rigorous in terms of the number of dives required to achieve the status. PADI requires a minimum of 50 dives. For NAUI's MSD, the minimum number of training dives is 8 (and one of the eight can be a skin dive). To earn the cert with NAUI, a diver could have as few as 18 scuba dives + 1 skin dive.
In sum, a diver is able to earn the NAUI MSD with a few dives and a lot of study/written testing on theory. To earn the PADI cert, a diver needs a lot of dives and far less study/written testing on theory.
I am not offering an opinion for or against either approach. They are different, and the differences simply cannot be reduced to blanket assertions comparing various ratings between different agencies.