Thanks for the information. Could you please tell me how reliable is the Insider Program and how different is it from the Windows 10 O.S?
On paper, Windows Insider is for early access to versions of Windows 10 on both PC and mobile before they are pushed to the public. It's divided into four rings. Fast, Slow, Release Preview and Production.
Fast and Slow right now are for the next version of Windows 10 Mobile and won't be available to your device.
The Release Preview and Production rings are the same right now, but the former should be a bit faster than the latter.
Reliability varies depending on luck, but the current stuff available to the 1320 (and most other devices of the same generation) isn't bad at all. The problem that arises is that the upgrade process may leave the device in a less-than-optimal state, so if it has issues after upgrading, hard reset the phone.
Otherwise, I don't think it'll be too problematic.