Diafine truly is close to idiot proof in operation. I've used it for many years to push Tri-X and more recently TMY-2 400 to 1250 and 1600. 3-4 min Bath A and B and you're done. The biggest challenge is not to contaminate the two solutions with each other.
With Tri-X you get very good classic looking results. But don't expect a miracle. You still are pushing a 400 asa film 2-3 stops.
TMY-2 worked even better, due to its linear toe, so you'll see a little more shadow detail vs Tri-X.
The best thing about Diafine is that as a two bath developer, it will go a long way towards not blowing out your highlights in high contrast situations.
Diafine improves noticeable after you put a few rolls through it. Once it has 'ripened' a little your negatives will become noticeably smoother and take on a pearly appearance.