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I must admit that it's a neat way to add a little extra juice and make a cheap PHEV. On the other hand, it's pretty useless unless most of your trips are 1-2 mile jaunts to the grocery store (in which case you should bike or walk).

100 mpg claims are completely meaningless without a mile range for that 100 mpg. Since they don't bother giving us a range, they're probably hiding an inconvenient truth. Let's try to estimate it. The Poulson battery pack is 12V x 120 Ah= 1.44 kWh. That's only slighly more than the Prius at 1.31 kWh. Since the Prius goes only a couple miles on the battery alone, the Poulsen PHEV could only do a few miles on battery alone too. Of course, that's not possible, since the car engine is always running.

So let's assume that on every trip you get 100 mpg (instead of 25mpg) for the first 5 miles. That saves you 60 cents per trip at $4/gal gas. At 3 trips per day, that takes you about 6 years to recoup that 4 grand. Sounds marginally OK. But wait....we forgot to add the cost of always hauling around 300lbs. That 300 lbs is dead weight after a few miles since there is NO regenerative braking to recharge it. Better save that money for your next car purchase to upgrade it to a real hybrid.

2004 Tideland, Package #7 (all safety options) + EV
70000 miles at 49.0 mpg avg.
Louisville, Colorado

If this were true the rest of your post would be spot on, unfortunately:

From: http://www.poulsenhybrid.com/FAQ.html

I noticed that Green-Hybrid is not the only place you have posted the same thing. Perhaps you should read a little more carefully before you malign a what might be a perfectly good product?

According to the article the battery pack is 72V x 120 Ah = 8.640KWH. Assuming 333 WH/mile (Prius is around 250 if I recall) that translates into an all electric range of 25 miles.

7 hp seems like a pretty puny boost for $4k. lead acid is also pretty uninspiring. I think I'll pass.

Sorry for the regeneration mistake.

I did read the Poulson page where it describes the system, and it did not mention regen there.
http://www.poulsenhybrid.com/poulsen.html
(Apparently you have to go to the FAQ to find that out.)
Also, I saw an unrefuted comment on another site saying there was no regen braking.

So apparently there is regen. That makes the whole system a lot better!
I would now say it's one of the best conversion deals out there.

As for the batteries, it says 6pc. 12V 120Ah. That might mean 8.64 kWh.
But Lead acid has power density around 30-40 Wh/kg. (Wiki)
Even if the battery is 250 lbs, that's only 4.5kWh (at 40Wh/kg).
So either 1.44 kWh or 8.64 kWh doesn't make sense. Which is it? Or where is my math error? Maybe they are using some great new Lead acid battery?

2004 Tideland, Package #7 (all safety options) + EV
70000 miles at 49.0 mpg avg.
Louisville, Colorado

Indeed. Some crazy companies are asking many times what a Poulsen costs for just a few extra batts in the trunk of a Prius. The Poulsen includes motor/generators and batts for only $4k. Plus a Poulsen will work with nearly any vehicle but some of the other conversions only work with HSD equipped hybrids.

Somebody is making a killing on batts. Check out these crazy prices:

http://www.hybrids-plus.com/ht/products.html

Wow, at those prices, it's definitely not worth it yet. In order to recover the cost within 250,000 mile, gas would have to cost $8.40/gallon for the cheapest conversion, and that's assuming you were always driving in blended mode and getting 100MPG vs. only getting 50MPG in the standard Prius.