I have a Delta 12-1/2" planer that I bought over 15 years ago (maybe 20). I had to replace the infeed roller recently but, outside of knives, that's the only repair I've ever had to make.
As for the 12-1/2" width, once I had a glue-up that took up the full width and I sent it through, I could hear the motor bog down. And it affected the results. I don't think these portable planers are really ready for prime time. IMO, they should be seen as maybe up to 8" planers for normal use. Usually, when you get wide boards you'll want to rip them and glue them up to make them more stable anyway so 12-1/2" or 13" really doesn't matter.
I've put all different kinds of hardwood through my planer. With certain woods you'll get chip out. From what I've read, the helical cutters reduce or eliminate this. So that would certainly be a feature that would increase the appeal of a planer, to me. But in the portables, I think only Steel City makes one. (Amazon sells it for $488.) If you work with figured or otherwise difficult woods, that might be worth looking into.
On the straight knife planer, my experience has been if the knives are really sharp you'll get a pretty clean cut. But once they begin to dull the results get worse, the planer begins to bog down, the infeed roller becomes strained. Mine are fairly cheap and easy to replace. But one nick, and you have to replace (or flip) the whole blade. The helical heads have a lot of four-sided cutters that can easily be rotated if one gets chipped.
