I considered the same, although I've only found Mobile 1 in 10W40, not 5W40.
Since the machine is still under warrantee, I decided to go with the BRP oil, and discovered that it is not a full synthetic, but a blend. BRP states emphatically that an oil meeting the API service SM or ILSAC GF-4 classifications will cause clutch slippage.
I had a discussion with the shop owner, who (unofficially) suggested that the Castrol 5W40 motorcycle oil should be a good alternative to the BRP oil. The Castol is full synthetic. The BRP "factory" oil does not indicate grade or service on the containers.
I intend to contact Castrol and see if they concur with using their "motorcycle" oil in a Spyder. Considering that a synthetic blend oil is typically about half the price of a full synthetic, the BRP oil seems a little pricey to me.
However, considering the complexity and expense of a Spyder, it doesn't make sense to go cheap on oil.