I have seen them used with mixed results. They can significantly increase the load on the GB and walking beam, have issues in cold weather and are not nearly as robust as the pumpiong unit driving them. Often the extra load requires upsizing the pumping unit which destroys the economics. In addition capacity control can be a issue. If there is no elec power they are probably a good sloution, if there is one should look at a small elec driven recip - quincy qrng