I don't own both, but I've read both, and I'd say that number 2 will probably serve you better. I think the limit hold'em section by Jennifer Harman is great, and it includes an Omaha section (whereas the first book had draw, I believe). Although the publisher recommends you get both (of course they do), I think the first one is pretty marginal in the extra material you get. SS2 is not an addition; it's a rework, imho.
As for the Omaha contents, there's one for Omaha 8/b of about 70 pages, and one on PLO high, for about 45 pages. What level of complexity they go into feels like a pretty subjective question, and I don't have a scale to answer that with.