It seems that this grill block is not very effective. The fuel consumption seem to have increased! With the last fuel tank, I drove 850km, and with this its aiming to less than 800km.
Meanwhile, I'll try this Ultimate Cell (UCCE). I'm still searching for some more reviews on this:
Ultimate Power | Energy Saving Technologies - Products
The Ultimate fuel and emission saving device | euronews, hi-tech
At 350€ is 4 times less than a GPL conversion.