A spin-polarized low-energy electron gun with high current transmission is described here and has been applied to SPEELS studies. Current transmission in excess of 40% is routinely achieved. This is a dramatic improvement compared with the $\sim$1% transmission obtained using an earlier electron gun. The high current transmission has allowed SPEELS studies of energy loss mechanisms in low-energy electron scattering from atomically clean metallic surfaces. There are two dominant energy loss mechanisms: dipole scattering which occurs in the vacuum outside the target and impact scattering via electron-hole pair excitation occurring inside the target surface. Preliminary results of SPEELS experiments on Cu(100) and Ag(100) surfaces and on thin films of Mo, Co, and Fe epitaxially grown on a Cu(100) are presented.