We had a Jolly jumper DS1 was not a fan and it was a pain in butt as we had to have stand and it was so big!! We borrowed an exersaucer from friends and DS1 loved it he used from when we got it at 6 month until 12 months. He would be in it for 15 - 20 mins at a time but would love it!!

DS2 we bought an exersaucer as could not borrow friends one again as in use, and it was great he was in it from just before 5 months. It ment he was upright and could intereact with DS1 as could play with toys on it together.

As others have said in moderation they are great, have not heard about exersaucers being bad for spine, Jolly jumpers I have heard mixed stories some say yes some say no, nothing is ment for dumping kids in for hrs on end.