Spring cot is not very good for your baby's back, but a lot of mummies here have different opinions on this. Some rely on this, some dont't.
Personally, I banned spring cot from my house, and even threw away the one that was handed down to me. Reason being I dont't want my girl to be used to being rocked to sleep, and I dont't want it to be a habit.
Anyway, some mummies use the spring cot to rock baby to sleep, then will carry out baby to the cot. While some mummies only use the spring cot for baby to take a nap.
I dont't think you should let your baby sleep in the spring cot for one whole night.