Our first-born slept in a portable crib up until 5 months old (always wrapped in a blanket, not tucked in) and in travel-coat up until 2.5 yo when we finally settled somewhere and got him a "real" bed.
We Didn't have any issues. As long as you are careful to keep them clear of toys, position them safely, and all other SIDS prevention-related practices are followed, there's no reason for it to not be "okay". Apart from your conscience, maybe, if you feel like it's akin to putting your child in a disposable cage. I was fine with that :)
Our second one slept in similar beds as well: portable crib until about 5 months old, and the same folding beyond 1yo.
Same recommendations: usual SIDS-prevention practices to follow to make the crib/bed a safe environment, and it's totally alright.