I found some inconsistent information regarding the Nikon DK-21M Magnifying Eyepiece
First, is it compatible with the D70? Some places say yes other mention another adapter then needed.
Does someone have an experience with it? Especially with glasses.
I assumes is won't fit inside the Ike housing.

I thought the Ike housings had a "big eye" magnifer for the viewfinder. The Nikon viewfinder magnifers will reduce your view. Check it out before you by one.

Thanks for the info, actually I'm thinking about this item for land photography more then u/w but as you wrote I'll have to test it before.

As an owner of both, I can say the DK-21M is certainly compatible with the D70. It does not require any adapters. B&H's recommendation for the DK-22 adapter is dead wrong. You could hook the DK-22 to your D70, or the DK-21M, but not both at the same time. I think the confusion might come from the fact that back in the good ol' days, pre-DK-21M, we D70 owners were using the DK-17M with a modified DK-22 to hold it on.

I do hear of glasses wearers complaining about the extra eye relief making the DK-21M unusable. Even with my naked eye pressed against the back of the magnifier, I sometimes lose sight of the corners of the viewfinder, which I don't mind at all.

I think you're right to assume that it won't fit inside the Ike housing. Good thing it has its own magnifier built-in!