As long as it's a safe sturdy seat, and he's unable to roll out of it, or slide down out of it, it's perfectly safe to sleep him in it! I slept my son n a portable swing a lot in the beginning (not on, just setting him in it), he would never sleep more than an hour or so at a time in the bassinet, so I dragged the swing into the bedroom, and he would sleep 3 or even 4 hours at a tme in it. I think the slightly upright position made it easier to keep food down, and helped a lot with breathng, along with mimicking the position in which he was held by me a lot. He grew out of it without any trouble, and it never became habit. Actually, at around 2 months, I began cosleeping with him, and he slept like a dream, flat on his back! The swing was just a really great alternative for us in our time of desperation and sleeplessness. As a new parent, you'll come to realize that even if something seems strange or unconventional, if it's safe and practical, it can save your sanity! Good luck wth your sleepy lttle man!!