The safety issue is not a real problem as all Oversize baggage is screened before loading on to the aircraft anyway. Due to their bulk, and the fact a thief would be conspicuous, oversized items are not likely to be stolen either.
That having been said, if you are carrying valuable items, why choose a Lo-Co carrier? Ever heard of a Lo-Co settling a lost baggage claim? ............ooh, look, a flying pig!!!