You can use any revocable trust as a gun trust.
The gun, firearms, or NFA trust differs from a normal estate trust by having language that deals with firearms specific issues and national firearms act specific issues.
I.e. What happens if someone on the trust becomes a prohibited person? Trusts merge?
There is a separation of liability issue to having some assets In one trust and firearms in another, but most people do not understand the actual protection that a trust provides and what tort protection it does not provide.
A firearms trust is also more limited in scope than an estate trust.
I often get asked about the quicken trusts, legal zoom trusts, etc. These can work. I have friends who have done them and have numerous transfers onto them. If set up right, they work well enough. Of course, if you have a question, you end up calling me or another firearms lawyer to answer the questions.
The free internet trusts have the issue of whether they are correct in the first place.
Now lawyer trusts, are generally more expensive than the internet trusts. But they can be more complicated and, in my case, you can call and ask questions about the NFA, firearms law or other trust issues.
So that is the basic. It's a free country. You pay your money, you make your choice.