I usually don't write reviews of a tool until I've used it quite a bit, but I'm going to make an exception in this case because there is only one other review. I would like to thank Jim, the first reviewer, as his comments inspired me to take the plunge and try this product.
This Hitachi NP35A is my first micro pinner, although I do own and use a few larger pneumatic tools (15 gauge nailer, 18 gauge nailer, 2 staplers). I typically prefer to use screws rather than nails, but there are occasions when the unique attributes of a power driver nail outweighs it's many disadvantages.
Here are my first impressions of the Hitachi NP35A 23 Gauge Nailer.
o compact, lightweight, and comfortable to hold.
o high quality product, for example magazine slides in and out with smooth precision.
o trigger is comfortable, double trigger is relatively easy to get used to.
o the soft nose tip leaves no mark whatsoever on even soft woods.
o very quiet, pleasant to use (no hearing protection needed with this little guy).
o easy side loading of pins, and automatically adjusts to different pin sizes.
o using the soft tip, appropriate air pressure, and good technique, pins are driven to a perfect depth just below the surface (the depth is adjustable via the use of a hex wrench on the nose piece).
o surprising nice blow molded plastic case.
o an easy to see bright orange "low pin indicator" (of course, it doesn't work if one is not paying attention and doesn't look at it ... just one of my many faults I'm afraid....)
o although the minimum specified pin length is 5/8", I was able to use the 3/8" pins without a problem (this is quite a good thing, for my projects).
o made in Taiwan (often a significant step up in quality compared to China made goods).
o the manual has a few typos (e.g. "all crews must be tightened..."), and it is bloated with the usual tedious and uninformative safety stuff (dictated by lawyers, presumably), but really, you can probably see that I'm nit-picking here.
I have tested this product primarily with Western Fir (actually harder than many "hard woods"), and a sample piece of 100 year old clear white oak (recovered from a badly broken desk). As long as one presses the tip firmly to the wood all pins are driven flush, although one does have to crank up the air pressure a bit for longer pins and harder wood.
I used Grex 23 gauge pins (since they come in a convenient multi-size package, available here on amazon for about ten dollars).
The longest pin length I tried was 1". This gun is specified to be able to handle 1-3/8, and I do not doubt that it will, but for now I can't see myself needing or wanting to drive these incredibly tiny, thin little needles into anything that would require longer lengths. However I know that many people do use much longer pins. Perhaps as I become more comfortable and experienced with this tool I too will join the super-sized crowd.
As you probably know, these pins are much smaller than 18 gauge brads, and much less noticeable. However, they are not invisible, especially in lighter woods. Nonetheless, they are much less visually distracting than their 18 gauge cousins. Also, if you build small things (say drawer inserts using 3/16" thick dividers) an 18 gauge brad is simply too big - it would split the wood - whereas a 23 gauge pin works very nicely (along with a bit of glue).
Hope this information is helpful to you.