I've done both for a long time.
Free diving for the last 25yrs, and SCUBA for the last 10 yrs (since I got certified)
I enjoy both, but SCUBA is a lot faster.
The SCUBA dives last for about 25-45 min each, depending on the depth, usually 3 per dive day.
The Freedive dives, last 4+ hrs and are very relaxing slow paced dives.
I can't perform like a 15yrs old any more, so a 2 min, 65 fsw dive, is no longer real for me, my freedives are a 10 sec 30 fsw dive and most of the time I'm scoping the reef from the suface in a very mild current if any at all.
With SCUBA, I can go where no one goes to fish and drop at 70 fsw for 25 min in the middle of the ocean in any current while using a surface float so the Cptn. can keep track of us, usually do these dives in teams of 2 or 3 divers at a time in the water.
To the new guy, I recomend learning SCUBA well, get some experience with the gear and familiarize with it before adding a gun to the mix, in my case I learned the spear before the SCUBA so adapting was second nature.
Try freediving if posible to get familiar with the gun and, that way when the 2 merge, it would be easy and SAFE to you and other divers.
The idea of instruction is a great one, I wish I had that option 25 yrs ago, I had to learn with a bunch of newbies that all had the perfect tip for catching the big fish, none of them dive anymore to my knowledge.
Spearfishiong is something that either you like it or you don't, try not to be some gunho with a gun that everyone try to avoid, be safe all the time, and treat a speargun as you would treat any gun.
Welcome to the brotherhood....................