That actually looks super handy, for anyone who cuts a lot if firewood that smaller stuff is a real pain in the ass - I get in way more sketchy situations trying to cut up small stuff and branches than big stuff.

Nice invention, on the other hand there would be in my opinion some modifications to be made in relation to the lack of security.
I think it would take a kind of casing that protects the chain in operation, perhaps sliding from bottom to top, along the length of the chain guide on either side of it. Which would lower when support with the piece of wood to be cut. To develop!!!
Or another idea of protection.
On the other hand, I find it very dangerous to go over the chain in operation to throw the cut pieces into the wheelbarrow.
Me, I think I would have put the wheelbarrow on my side.
I allow myself to make these few remarks because myself, I am quite a "do-it-yourselfer", it will be said, and it also happened to me, to make some rather hazardous "inventions", and see, dangerous!!! !This is in no way to make a personal judgment.

One suggestion is to lengthen your relay ( center) arm. Or change your pivot point .So your wood is against your upright and only enough tension on pvc to keep throttle at proper position.
You won't be fighting the chain so much or risk breaking the plastic throttle by exerting excessive pressure and vibration.
As always be safe.