I don't think I can get more specific than what I already said, that I can get two days' flying with a gallon of FAI or 5% nitro, flying 4-5 flights a day, doing a double round of IMAC Basic each flight. I am flying 14-15 lb (6--6.5 kg) quarter scale aerobats on Moki 1.80's, full throttle on uplines, idle on downlines and about half throttle on straight & level, typical IMAC throttling. If you have a warbird or large scale model and fly wide open throttle all the time, that will use a lot of fuel pretty fast. Also, the low-speed needle on a big two-stroke glow will affect fuel consumption well up into the mid-range, so low-speed tuning is important to good fuel economy. I will grant that running rich on the first few gallons for breaking in does suck up a lot of fuel.

As to the petrol version, my understanding is that the glow engine known as Moki/Mark made in Hungary is completely separate from the petrol Moki, which I'm told is made in Germany, no connection to the Hungary operation, apparently just riding on the Moki name because of lack of trademark registration or some such issue. I have not seen a Moki petrol engine other than in pictures, so don't have any practical knowledge of them.

I would expect a glow engine to burn fuel at a higher rate compared to a petrol engine of the same displacement, but it would also deliver more power. I don't know whether there is a Moki petrol engine of 1.8 cu in displacement (30 cc), but if there is, I would expect it to deliver considerably less thrust compared to the glow powered engine. I do own a couple small MVVS petrol engines that I fly with tuned exhaust, but without tuned exhaust you really need to get to 40 cc displacement and larger to get good economy with petrol.

I guess I'm lucky in having an active group of flyers around, so I'm usually not the first to try something new in radio control. I can watch other flyers, talk to them about their equipment, and satisfy myself before I invest time & money in something unfamiliar or unproven in my own experience.