About Iphone 5S in general: value for money at the price I bought(though I suspect prices will go down further).
Differences with iphone 6 are marginal at the best and are probably meant for more discerning users. The 4 inch screen would appeal to those who want great performance and a "manageable" phone size.
Also, you would get auto upgraded to IOS 9.2 during setup. For people moving from Android, there is cool feature which allows seamless transfer of most of the data from old phone to your new iphone.