A bit fast, I think. And anyway, AIUI variable speed is a useful feature - fast at the start, then slower once the meat starts to brown.Is 8RPM good enough for turning?
Also there's the issue of how are you going to mount it? How are you going to shield those wires from the heat of the BBQ?
How are you going to connect the shaft to the spit?
You're going to have to buy quite a bit more stuff and do quite a bit of mechanical construction to be able to use that motor, which will need to be well done or it will jam, and I can't help noticing that despite the title of the item, in the body it says "Widely used on auto shutter, Pan/Tilt camera, Slot machine, Money detector, Coin refund devices, etc." - nothing about ovens, BBQs etc.
My advice is to abandon the project now, while you've only wasted £8.40, and look for a purpose-designed complete BBQ spit accessory.