Mobile tariffs - am I missing something?

[boyse7en]

I've got a really naff (£2.50!) Samsung mobile on Orange PAYG which i'm thinking of upgrading to a MotoG or similar on a basic monthly tariff, as i think it will be cheaper overall (I seem to top up £20 every 6 weeks or so) and won't run out of credit at critical times

I looked on Tesco mobile site, and the cheapest MotoG contract is 24mths @ £10 per month for 250 mins, 5000 texts, 500Mb data, with no up-front cost for teh phone
So then I looked at Sim-only deal, and the cheapest is £10 per month for 250 mins, 5000 texts, 500mb Data, obviously I'd have to buy the phone

Seems a no-brainer to go for the Phone with contract, as it is the same price with (effectively) a free phone, or am I missing something?