That's right, now that you mention it, I can also remember that these free bets can "only" be used for single bets and therefore do not offer the option of combining several sports bets into a multi bet. Unfortunately, I can't try it out at the moment because I've already used up all my free bets.

On the one hand, this is understandable, as you could win very high odds with a lucky punch (combining five bets that actually come true). On the other hand, the probability of this happening is of course very low, so in terms of the house edge, it would certainly be acceptable.