Thanks to Martin at Fjäderlätt, I now have the weights of gas used for the Gnat on the recent trip to Vålådalen.
The stove was only used for boiling water, and a windscreen was used some of the time, the design of the windscreen came from BPL.com and information can be found here.
The total amount of water boiled for the 3 days was 4 litres approximately, the amount of gas used was 80 gms, indicating that 20 gms of gas per litre of water boiled was used. For me this would mean that I would use less than 30 grams of gas a day and with the weight of the stove (48 gms), the on trail weight has similar figures to that of esbit and alcohol. In the end the difference may be a matter of the weight of the empty gas canisters when compared with the weight of the bottles used for alcohol or the packaging of the Esbit, an interesting conundrum.