Product names and model numbers come in all shapes and sizes. You've got long ones you can't even remember, to very short and concise ones. Fortunately Synology falls in the latter category. The DS114 and DS214 we're looking at today would seem to be closely related, one with two and one with a single hard disk, but there are more differences than meet the eye.
The first number indicates the number of disks while the second indicates the mode year. Sometimes Synology devices also carry a suffix in their name which indicates the positioning. The 'j' was reserved for the budget models for a long time, and more recently an even cheaper model came out called the DS214se.
Of course having two disks mirrored in RAID 1 is a safer solution, but if you can arrange a back-up in a different way the single-disk DS114 could be a good option, considering the two-disk model costs about £80 / €200 more.