If by "nitro" you mean glow fuel, then the answer is: it depends on what glow fuel you use - just like all glow engines. 15% will be consumed faster than 0% nitro, simply because nitromethane has a lower stochiometric ratio than methanol, so you'll burn more fuel per combustion cycle with more nitro in the mix.

I don't think the Ryobi guzzles more glow fuel than the typical 1.5 to 2.0 glow engine. Stay with 5% nitro and 10% oil (Super-T fuel) and you can easily get 15min of flying out of a 16 Oz. tank. I would go with a 20 or 24 Oz. tank though.

I'd say don't get the engine if you just want to save a buck. If you don't have any experience with tweaking a Walbro carb, you'll be lost. If it doesn't come with a Walbro WT-499, which is the one that Zenoah uses with the G-23 glow, ask the guy what he did with the carb to make it glow compatible.

Conversion engines can be a lot of fun to play with, but if half of what I said above is greek to you , get a regular glow motor instead.