They have a free DVD (from PSI) about the duplicator ... that should tell you quite a bit about how it works. I'm certain that you could mock up a jig that would accomplish the same purpose, but having one ready made to fit your lathe and is good to go? I think it's got a nice price point, as an additional accessory for your existing lathe, if you already have one that it fits.
I don't have the penpal, but from what I'm told and what I hear, it's quality is a decent step higher than the Harbor Freight Mini Wood Lathe 8x12 with 1/3 hp and variable speed dial control. That's what I have and use, and I've had little trouble with mine.
If the amazon review said "10 days", I'ld assume working hours of 6 hours a day, so 60 hours of use ... I'ld also assume that since that appears to be a 1-off, it was just a manufacturing fluke. I'm pretty sure PSI would work pretty hard to fix that person's issue, since they like to stand behind their products.
The penpal comes fairly well equipped to turn pens, keychains, and other small diameter projects. I would think that it would handle candlesticks, small bowls, teacups, saucers, goblets, and bottle stoppers as well, up to about 4 inches diameter. It's power should be comparable to the Harbor Freight Mini that I own, perhaps a little better. Mine's 1/3 HP, theirs is rated like 1/2 HP, so it should have a little more power for turning slightly larger stuff.
PSI also sells replacement motors that fit not only their lathes, but some that fit generic mini lathe models AND include variable speed control. For about 150 dollars, you can get a 1/2 HP motor + variable speed control box to add to say ... a Rikon or Nova midi lathe that has belt speed change only, and make it a variable speed (motor speed control) lathe. You could even incorporate the upper (spindle) pulley wheels to change your speed range even further.
editing - as an addendum:
A bit more about the duplicator...
It's tailor made for duplicating exact replicas of existing pieces.
If, for example, you wanted to turn out a set of chess pieces and have all the pieces that are of the same type come out looking EXACTLY the same.
Or, if you wanted to create the same exact profile on all of the pens of a single particular set or line of pens... duplicate the profile to a point just before finishing, and then sand and finish by hand.
If you want to create more of a "production line" rather than "hand made" products by incorporating a duplicator, well ... the beauty is in the eye of the beholder. You'll have a lot more time in the end for finishing your products and be ensured that they all reach that point in the most efficient manner possible, but it does take away a bit from the "made by hand" field of work.
