Just check the weight restriction, my older son was a big boy and only 23 lbs by 1 year, just for reference. He used it until he was about 7 months though. We used it for his 3rd "cat nap" in the evening, until he started to look too big and also needed to be in a more quiet space. You could always check craig's list or a local mommy garage sale group to find a cheaper one if you are worried about wasting the money.
DD only liked being in the swing swaddled for naps but within the past week hasn't liked it at all. Just depends on your LO's preferences. She is 8.5 weeks.
Babies often stop liking the swing when they are sitting up on their own. So 6 months or more. We used ours with DS a bit longer than that. So I think it's worth it now, especially if you find a good deal.
Re: Too late for a swing?