I'll admit I have an old logic analyzer, with an old pattern generator, but it can be programmed in 'C' to generate whatever stimuli are required and in response to just about any combination of outputs from the circuit under test.

I don't know how the hardware to which you refer is supposed to work, nor do I know how it differs from what I use, as mine is just an attachment fixture between the LA boards and the circuit under test, which then requires that provision be made for it in the initial design.

The LA I use has a 68030 at its core, so that limits, somewhat, what the box can do, or, at least, how quickly it can do it. Once programmed, however, it does what's asked of it. I assure you that is specifically capable of testing complex state machines, as it is entirely programmable and has done so many times. It's true there are automatic test machines that can do the job faster and, perhaps, better and more thoroughly, but this thing has served well for a decade and an half or more.

I'm not sure how iterating through 2^128 steps would help, either. If you know what you're testing you can design the test to prove what you intend and to show where it fails. What more do you want? I can perturb the power supply and I can cause the clocks to drift. I can inject noise of programmable magnitude onto this signal or that. I seldom have to do that. I do sometimes have to test boundary conditions, which has proven useful.

RE