The only direct offer comparison I could find was with Virgin Mobile's $29/month plan, which also has a $0 upfront payment to get the same phone over 24 months. The main difference here being that Virgin's deal includes 250MB of data each month, while with the Vodafone offer only gives you 200MB. So if you're more of a talker than an internet user, you'll probably be better off with the Vodafone deal as the cost per 2 minute call is $2.36 vs Virgin's slightly higher charge of $2.38.
But over the lifespan of both contracts, the Virgin Mobile one will cost you $696 versus Vodafone's $630. So basically you'll need to estimate your usage costs with Vodafone over the 24 month period to see how likely that price gap is to close.
VODAFONE: standard voice calls=98c per min (+40c call connection); standard SMS=30c; 1MB Data=10c
VIRGIN: standard voice calls=99c per min (+40c call connection); standard SMS=28c; 1MB Data=20.5c
(Note, this Vodafone offer expires on the 26th of May)