Hello Tucker and Welcome!
Really good question! As you point out, the primary reason for the 40hr option is to give the student the opportunity to save few dollars IF they plan on instructing for ATP. Back in the day this option wasn’t offered because there was no 1500 hr Rule. Before the rule change you simply needed your Commercial license and as little as 500hrs total but there was (and still remains) a requirement for 100hr multi time to get hired at a Regional. Instructors were only teaching a few months so having the 100hrs enabled them to check that box immediately. Since the rule change Instructors at ATP will be there a minimum of 1.5 yrs working towards the 1500hrs and since much of the training at ATP is done in the twin, getting the 100hrs multi isn’t really a concern. Makes sense yes?
So is there any other reason to go for the 100hrs? I believe there is. As I’ve mentioned in other posts, most pilots simply see instructing as the means to an end (which I understand, I did too), but instructing can be very challenging and sometimes even a little scary. The fact is more pilots find themselves having a REALLY bad day in a twin that loses one engine than in a single that loses it’s ONLY engine. Now this should sound counter intuitive since in the twin you still have one good engine and you can essentially keep flying. Problem is when that engine first goes out some funky stuff happens initially and if you’re not on it rather quickly it could be a problem (that btw is the primary focus of your multi training). Now with the 100hr option you’ll do your Instrument training (arguably the toughest rating) in the twin (a complex airplane) which gives you a fair amount of practice multi tasking in the multi engine. You’ll also get to do your cross-country flights in the twin which (because of it’s range and speed) will allow you to travel farther and see variety of flight conditions (weather, terrain, etc) that you wouldn’t otherwise. This gives you tremendous confidence and comfort in the twin (aka a complex airplane). What this means is the first time your student does something incredibly foolish, seemingly trying to end both your lives, I believe, you’ll be that much more prepared.
Now let’s be honest, $10k is alot of cash to get the warm fuzzies and truth be told if the 40hr option were available back when I signed up I probably would have grabbed it. I’m also not saying the pilots who take the option are lessor qualified or inferior pilots. What I am saying is, knowing what I know AND having been through the program and flight instructing, if I had the money to do the 100hrs I think it’s a worthwhile investment.
Adam