yeah dusky, i guess if this is a hobby and giving you something to do then i suppose this would be something worth puddering around with (so to speak) ;o)
I've been a tech for many years and built many engines and have even gone through diesel school (years ago) so something like this would catch my curiosity as a project too.

But i too tend to agree with what that site said about economy savings... are you actually gaining any savings? You may be gaining 'diesel fuel' savings by injecting the lpg into the combustion chambers to help burn the 'unburnt' fuel and pick up some extra horsepower in the process. But are you really saving money though? (i am going to assume money savings is not your goal here, or is it?)

You are dealing with 2 fuels now instead of one and given the ratio of diesel v/s lpg being used per gallon per mile and just having to now buy 2 fuels for this vehicle...
are you actually coming out to the better? Can you understand what i'm getting at? The cost of savings on diesel fuel is offset by the cost of purchasing the lpg fuel so your not really saving anything. Based on the age of the engine the fuel consumption varies, the newer engines with all the emission controls are alot better at burning fuel so the burnt to unburnt fuel ratios would not be in the range you speak of,they would be considerably less, so i assume your engine is an older one. So adding lpg injection may help in that department somewhat but if a decent exhaust system, top grade fuel and adequate adjustment to fuel delivery and timing is applied the engine would burn most of the fuel anyway. One of the biggest enemies of poor fuel consumption on diesel engines is poor compression (worn rings), poor injection(faulty injectors), dirty air intake filters(lack of proper air), and incorrect timing and of course poor quality fuel.

You're probably saving the environment somewhat by eliminating the polution being created by the unburnt fuel emissions which is a good thing i guess but as for economy savings i just don't see it from my point of view.

The one thing everyone can agree on though is you do get more power out of this added component for sure... everyone seems to agree on this point. ;o)

But being a hobbyist project i can see the attraction to doing this...
i myself would probably try it too ;o)

good luck and let us know how it turns out once you get it installed and dialed in (so to speak) ;o)