Repair some weather battered garden table, bench and chair set  

These types of repairs are cosmetic only and will not restore structural integrity. They also tend to be relatively short-lived exposed to weather unless well protected by a proper film finish or paint job. If it's minor surface rot, OTOH, this technique may be viable. A few pics might help.

If you're talking about the Minwax (I think?) wood hardener and expoxy filler, I say go for it.  I used that stuff on rotted window frames in a 1910 house and it's pretty amazing.  I used it on an exterior door frame in the same house where I had to put a new lockset in and the old holes didn't match up at all.  A carpenter told me that the filler would shrink after awhile and gaps would open up--well, it didn't and the door still looked and functioned like a solid piece of wood years later.  
That's been my experience with this stuff.  I'd try it if I had what you have.
 

For the past couple of years, I have used a wood repair system by Abatron.  As with any wood rot systems, I am never really happy with their staining abilities, but, since you are painting the set, I would highly recommend their WoodEpox system.  It doesn't shrink like Miniwax and is easier to work with.  It is a two part system that once mixed in equal parts goes on like a dry Playdough.  It also sands up nicely.  

Abatron---I think that was the one I used!  It was highly recommended by The Old House Journal 20-25 year ago.  Though I think Minwax's Wood Hardener and expoxy filler is the same kind of thing (not to be confused with their regular wood filler, which isn't really good for much in my opinion).