Basically they're the same thing.
A lot of what ATF does is up to how they interpret it today, which can change tomorrow. Removing a co-trustee or responsible person before submitting the application and then putting them back on later is open to interpretation and argument every day. This may well work out for many years to come however what ATF interprets tomorrow may be totally different then today, see bump stocks, see pistols with a "brace".
If something would happen to you after you removed every co-trustee or responsible person except yourself, and before your application was approved, you could be screwed, depending on how the trust is worded.
We all know the intention of ATF was to have every co-trustee or responsible person to have a background check done, and their gimme was no LEO sign off. Removing co-trustee or responsible persons then putting them back on later is avoiding this. Not saying its right or wrong, or how the trust works, but it's open to debate, even lawyers have different opinions on this issue, or how any given lawyer interprets it. ATF rules can be confusing even on the same subject.
There are other ways to transfer NFA items after your death, even with having a normal Living Trust and not a NFA Trust. This is why I don't like internet trust sites. See a trust lawyer in person who has knowledge about this stuff and will be there when you die to cover your families ass if ATF interprets something different later on.
My situation my be different then yours. I don't have all my stuff in NFA trust, I have one item that was done before the rules change, but my family will still get my NFA stuff if they want it when I die, if not it can be sold. That's what I have a lawyer for.