MM3 Kim has made some excellent points.
Enlisted boot camp and the basic military skills gained there and at subsequent schools and assignments are a great base to build on at USNA -- just knowing how to spitshine shoes, prep uniforms, make the bed correctly and have general and technical Navy knowledge is a nice bump that delivers a precious commodity, time. That familiarity with military life, especially enlisted, allows for leadership skills to quickly develop. The majority of the class will not have that basis, though, but generations of plebes have handled those challenges and come up to speed quickly. NOT something to pin a decision on, IMHO.
I have known many prior enlisted who came via the nuke path to USNA, but the majority of them did not plan it that way -- the USNA opportunity was mentioned to them, they took the test, and next thing they knew, they had orders to NAPS or direct to USNA.
There is some risk involved. The "needs of the Navy" will always come first. If the Navy needs you more doing an enlisted specialty they are undermanned in, that's where you will go. As MM3 Kim noted, the Fleet seats are usually not fully taken, so there is a definite window of opportunity.
And, there's many a slip between the lip and the cup -- there could be an injury or some other issue that pops up that precludes a commissioning program but would not hinder continued enlisted service.
If direct admission and NROTC do not work despite repeated attempts, taking the enlisted path is a viable but not guaranteed Plan C. And, there are many other enlisted-to-officer programs that do not involve the Academy. Especially for those who hit the age ceiling, have kids or some other issue, there are several programs that pay for college, either full-time with ROTC, or part-time, with commissioning via OCS. There are even those who do enlisted time, get out, use GI Bill and VA benefits to get college degree, apply for a commission and come back via OCS or direct commission (have seen this for chaplains, former medical corpsmen who went to med school, lawyers, etc.).
As usual, this often shakes out to a question on what the goal is: serve in the Navy/Marine Corps no matter officer or enlisted, serve as an officer no matter the path, attend an SA .... Put in this context, the SA is a means (turbo-charged!) to the end, serving in the Navy or Marines as an officer -- that goal is the over-arching one.
Don't give up on the SA or ROTC route. There are many threads on here which comment on those who tried several times and finally got in, impressing the Admissions Board with their perseverance and commitment.
Serving as either an officer or enlisted is a win-win, in the largest sense.
“Any man who may be asked in this century what he did to make his life worthwhile… can respond with a good deal of pride and satisfaction, 'I served in the United States Navy.'” John F. Kennedy Darn tootin', say I!