The hardest part of this build is getting the fuel ratio right between the flame holder area and the main airflow, and the maker is attacking it head on. Rather than running calculations, they openly admit to winging the design, sketching a cross-section that maps where the tiny and medium fuel streams should sit. Where the main flame front will end up is still the big unknown, and they seem fine finding out by testing.
The construction so far is tidy. The flame tube is brass joined with stainless steel rivets, and a single brass tube will run down the center of most of the afterburner, feeding fuel through radial holes to both the flame holder and the main flame. The flame holder itself has air inlets at the front plus adjustable petals, which gives a tuning path if the flame refuses to stay lit. Fireproof material will separate the tube's outside from the plane's foam, which seems like a smart call on a foam airframe.
The whole thing is meant for a Horizon Hobby Viper style 64mm airframe, and the maker is clear that it is purely for looks, adding zero thrust. The aim is a very clean cone of flame out the back, capturing some of the fun of big turbine jets without the cost, hangar space and maintenance.
There are honest trade-offs here. An 8 ounce butane can likely buys under 30 seconds of burn, so flights will be short bursts only. Nothing works yet either; whether the tube can hold combustion at all remains unproven, and the rivets still need sanding down before the next stage.