Browning ~ It really depends on what range of orphaned sources you're talking about. Both the UltraRadiac and RadEye-G are compensated G-M's and aren't the best pieces of equipment for detecting and interdicting orphaned sources. The UltraRadiac is a commercial version of the military's UDR-14/15, which are CBRN response devices intended for battlefield situations where high dose is expected. The UltraRadiac is slightly more hardened than the RadEye-G, so it will response somewhat slower to very low intensities and energies of gamma/x-ray.
There is a version called RadEye PRD that uses a NaI detector which can supposedly see down to 30keV and will respond quicker due to the lower specific ionization of the scintillator. We could only test down to 60keV, but the RadEye PRD demonstrated a quicker response over any of the G-M based PRDs. The one downside is there is no G-M backup, so it overloads at 25mR/hr. Not a problem when selecting soley for detection and general location of a source.