I have some questions for you:
How old is your niece?
How heavy is each machine?
Which one is easier to thread?
Is one more intuitive than the other? Dials easy to understand?
Which one is quieter?
If you don't need two machine, why buy two, just because you can? (Having been guilty of buying ones impulsively because they looked good/were cheap/claimed they'd be my backup--who needs 7 backups?--I say think about which is more important--the machine or the real estate it takes up and realistically how much use will it get?