I don't know what you mean by "a bit heavy duty", but it has to be able to widthstand the shock forces generated in the diff which are much higher than in a gearbox. It's the correct viscosity and is intended for use in LSD applications. You only need an LSD additive if the oil isn't desigined for LSD use and needs to be boosted.
Here's the blurb from the link I attached:
"Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended."
Sorry Matt, I don't mean to be thick, I just can't help it
By heavy duty I mean that this oil is call SEVERE (in capitals!) gear oil designed for use in very heavy situations. I read the blurb but the specs mean little to me so is one of those a spec that says it is designed for LSD use.
I've never had an LSD before so it's a bit confusing for me!