I have one and as everyone else has said, it is a valve-spring compressor, but I think it would be too light for serious use as a proxy G-clamp.
I do use it thus but only for gentle forces, usually on rough woodwork such as temporary supports..
Even a regular G-cramp can be distorted if used too cack-handedly on uneven surfaces, and I have encountered clamps so abused, often with the foot missing as well, finding them very frustrating to use.
It is hard to think of other alternative uses for a spring compressor, and it's probably better to find it a new home with someone who can use it for its intended purpose, in servicing vintage vehicles.