This was advertised as a JA 850 Ross Yoke Stirling engine. I'm not sure if JA is the maker or maybe it's someone named Ross Yoke! I think Ross Yoke is the name of the special linkage used, not the maker. It is a low temperature hot air engine. The usual 90 degrees phase difference between the power piston and the displace is determined by a rather clever linkage, which is what I think is called a Ross Yoke.
It is a low temperature type with a large area displacement cylinder, which is intended to be heated by standing on a cup of hot water or a similar heat source.
The displacer constitutes the base of the engine and is 100mm diameter x 15mm high. The displacement piston is made of light weight foam material. The top and bottom plates are made of transparent plastic (presumably Perspex).
On the top plate is mounted the support pillar for the flywheel and linkage, and the aluminium(?) power cylinder. The power piston is 13mm bore x 8mm stroke. The crankshaft has a single crank which is connected to the power and displacer pistons via the Ross Yoke linkage (see the video for how this works). The flywheel is 118 mm diameter and of lightweight construction. Despite it's light weight, it gives the engine a very smooth action.
The engine works well sitting on a cup of tea, although it won't work by the heat from a hand, like some will. I haven't tried it yet on a block of ice to see if it runs backwards!