If it's a magazine I subscribe to, then multi-part isn't a problem.
However, if it's one I only see a few times a year in a shop, then I might (or might not) pick it up if it's part one, but will most likely skip it if it's part two. There are exceptions to this rule, but that will very much depend on the article.
Magazines that make a habit of having multi-part articles are magazines I tend to avoid

But, yeah, as Dice Roller mentioned, checking magazine policy is probably the best place to start.