Hey all, has anyone looked into or executed on a self-directed IRA for investing into deals?

I'm specifically NOT asking about ROBS 401k because that's a very different tax/financial structure with pretty big downsides, both reporting and structural.

I don't know if there are difference between a self-directed IRA or a self-directed 401k, but initial research is showing that the IRA option is the most flexible since you can just roll existing IRA into it to get it off the ground. Versus self-directed 401k that's tied to self-employment income for current or past years.