I've used it before with no ill effect.
Everyone says you shouldn't mix oils but as it's "just" airborne in the petrol vapour, hardly under the sort of stress oil in a 4 stroke is and burnt about 1/100th sec later I wouldn't worry about it too much as long as the base oils can be mixed and wont react to each other in the oil res.
It's certainly better to use something cheaper and then change back than nothing at all if caught out somewhere and I've never seen a stroker suffer the same problems as a 4 stroke does if you changed from a mineral to a castor based oil or vise versa*
When I first got my Aprilia I had no idea what I was doing and mixed oils with zero concern, never used the cheapest stuff but anything semi or fully synth went in, it still worked.

*A friend of mine flushed his Castrol R running engine out with normal engine flush and put Castrol R back in again, bottom end started knocking about 15 mins later and when I stripped it down (after I finished laughing at him) there were big blobs of what looked like soild wax in the sump and clogging the oilways.
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