Hey guys, Im curious what you guys think of this idea.

I'm considering the possibility of marketing some of my projects to other companies that I do business with.

For example I'm developing a mechanism to open, sort and stack certain chemical containers when they are mixing chemicals to service a gas well.
All the design work, fabrication and testing is done by my shop however the company that this device is for is paying for the prototype costs.
They have merely given me the concept of the device and the parameters with which they expect the device to operate in.

Is it legal for me to try to sell the finished product to other companies?
Is there intellectual or other copyrights protecting the original client from me doing this?
If so, how do I go about obtaining legal rights over the products that I build and develop?
Do you guys think there is an ethical issue with me marketing a developed product to other companies?