hi bruce,
i use the angled inon viewfinder for a year now and also looked through other angled viewfinders underwater (seacam) and also checked the straight one.
inon straight and angled give the same image in the viewfinder.
in the beginning finding things through the angled finders is much more difficult compared to a straight one. but after a while the advantages of the angled one beat the straight one ... you are much more flexible and can take images you just can't take with a straight one (at least not without destroying the reef). also you get used to the angle very fast and when i tried another straight finder a while ago i had the same effect again ... i was looking on the wrong spot, because i was so used to the angeld one.
compared to the inon finder the seacam finder is a bit more comfortable ... i must admit that. harald from seacam let me try his viewfinder on a dive and we swopped cameras. after the dive i told him, that his viewfinder is much more comfortable and he told me, the inon is better than he thought ... so the seacam is (as expected) the better one, but the inon offers good value for money.
if you decide betweed the two inons and shoot mainly macro: go for the angled inon.
i dont know about other viewfinders on Nexus housings. i think inon is the easiest way.