Oh they're quite different. Enough so that some very sophisticated Basenoters enjoy one without caring for the other. The oil is far softer and mellower than the EdT. (Or is it an EdP?) The scent seems somehow smoothed over by the almond oil base, and it expresses mostly the middle and base notes of the EdT with none of the sharper top. The oil doesn't project much and doesn't seem to leave much sillage, either. It has been called wimpy compared to the EdT and its lasting power is very limited. On the other hand it is very useful when you want some of the Musc Ravageur experience but don't want to be as conspicuous as the very potent EdT can make you.
If you're only going to get one, I say go for the EdT. It's a fuller experience of the scent - more complex, more nuanced, and more lasting.