Is it better to have no publication than having you as second author?

If the paper is well-written, contributes non-trivial knowledge to a particular field, is peer-reviewed, and you contributed significantly enough to the paper to be listed as an author, you should put your name on it. In the case of fields where pre-prints are common (i.e., it won't be peer-reviewed, at least initially), it is also worthwhile.

What you don't want is to be an author on a poorly written paper. In other words, you should be proud to list a publication on your CV even if it isn't exactly in your primary research area. Especially at this stage in the game, having a few good papers will help your case, even as a second author (and keep in mind that some fields, such as theoretical computer science, should have the authors listed alphabetically and all authors are considered primary).

In my opinion, I would evaluate the quality of that paper (so far) first. If the quality is good, I would join him and become the second author. If the quality is poor, then walk away.

You have only one publication thus far. Have another one, even the second authorship, is definitely better than nothing. Not to mention your first authorship paper is not very good by your own evaluation.

In the end, each paper counts. I would not hesitate to get second authorship unless I felt I deserved to be first author on the paper. What you need to consider is if the time you spend is worth it. If the paper is going to a good journal then is more acceptable than if it goes to a low rank journal. When your cv is evaluated, number of papers, journal impact, and citations on the papers are most frequently looked at. First authorship is an important factor as always but having second authorship (I am assuming among several co-authors) shows that you have been instrumental in the paper (I am again assuming authorship order reflects contribution). As long as you have first authorship on a sizable fraction of papers no-one will think twice about coauthoships, particularly not early in ones career.