Gel fires are quite new in the UK, we have tested a few of them. They are nice products with a big flame however we all feel they are more suited to outdoor useages, the reason being is the ethanol can create a slight odor when burning. Its not that noticiable but depends how sesitive your nose is. Secondly it is a bit messing around to fill it up everytime you wan’t to use it. The maximum the tank will last for is around 2.5 hours. 
As far as cost wise, Ethanol is cheaper however, it is more expensive to package and transport while LPG has the benefit of econmies of scale selling thousands of tanks a day. In the end an gel fire will be 100% efficient, so all fuel turns into heat, while there are high efficinent LPG models out there it will not be 100% unless your going flueless catalytic. I’d say the amount that would be saved by using a gel fire would certainly be taken in time spent filling it up and disposing of the bottles.there are many ways to increase your efficiency;
1 Catalytic Flueless gas fire (100%)
2 Balanced Flue Gas fires (circa 89%) [with extra large heat outputs avaiable on selected models]
3 High Efficiency Glass Fronted fires (circa 89%)