If you can somehow make 0 buffer have instant aerials, awesome. Or if you can make 1 buffer not have this crouch after fast falled aerials, that works for me too.
First things first, I agree with this if it can be done.
But I'll take 1 buffer over 0 buffer even with the crouch because, in the end, both affect the SHFFL. One affects the end, one affects the start. Some characters can't even SHFFL without that instant aerial, so I much prefer having the possible crouch because, in my testing, actually getting the crouch is just a matter of timing.
So let's move on to that point:
There are probably other characters that do as well but I'm not gonna test everyone. If you're fast falling these without crouching afterwards then you're either flicking the control stick very lightly for a fast fall, or you're just letting go of the stick really fast because that's the only way it's possible. I think the best way to describe it would be that it's like doing an Utilt with tap jump on. It feels unnatural for a SHFFL.
It's funny because the way you describe it makes it look like the 1 buffer is actually adding more skill to the SHFFL. You need to time everything properly if you're going to avoid that crouch.
For me, I never had a problem. I can SHFFL all day long at 1 buffer. I guess I just got used to the timing.
It's like how people say you should spend half and hour with 0 buffer to get used to it. I'd say it's a similar case for 1 buffer, but with better results (since you keep instant aerials). With enough practice, you can nail the timing all the time.
So I dunno, from your opinion on it, it's looking like 1 buffer is making you need to be even MORE precise with your input timing than 0 buffer. And isn't that what people wanted 0 buffer for?
Try doing what KayJay said and using the Cstick for a fast fall. I use it myself and it works well. It's good because the Cstick input only gets read once per flick. So if you flick it down during your aerial, you'll fast fall and won't input another command, so there won't be another command buffered. You follow what I mean?
If you keep mashing the Cstick down, you can then possibly get the crouch if you mashed it enough. But it's a lot less likely to happen than in Vanilla Brawl, when I would always get the crouch by mashing the Cstick down. (In fact, mashing the Cstick down in Vanilla I would get the crouch AND the Dtilt instantly upon landing. It was actually very useful for Sheik. ^.^)
Give it a shot and see what happens.
1 buffer only makes the crouch happen if you let it. It's all about timing, and isn't that what we want more of in the end?