I've used the IF Binoculars for probably nearly 20 years now. Absolutely love them!!
Leupold used to make them. My old Leupys are 10X40's. I bought some Steiners after that (10X50 NightHunters) and have used them too. I still have and use both and will never lend them out or sell them. A good friend has another version of the Steiners with IF and he is really happy with them too.
Once each eyepiece is set for your eyes.....you never have to focus them or turn a knob/diopter ever again (unless your eyes change). From 20 yds to Infinity, they are good to go!
Only thing is, when you do the original focusing, do it on something very distinct with shart edges and contrast, and do it at beyond 100 yds. Also, as previously stated, fine tune with both eyes open. Once that's done, leave them alone and enjoy them.
I can look through mine for hours and hours straight and never get any eye strain or headaches, I can honestly say they are pure pleasure to use.
I also have some regular binos and I do get eye strain with them. I always have to re-focus the center wheel for distance and everytime I do that, it seems the diopter needs changed one way or the other some too. My regular focus ones are also Leupold and Steiner. I've even looked through some swarovski bino and still felt that something wasn't quite right with the normal focus/diopter. Maybe it's just my eyes, but give me IF anyday!
For me, these IF binos are like Jewel triggers, once I tried them I'll never go back. I don't know why Leupold ever quit making the ones they did, but at least Steiner is making them. Get em while you can and if you like em as well as I have, don't get rid of them, ever!! I'd give up one of my $6000 custom rifles
before I'd give up either of my IF binoculars!