Thanks for the feedback everyone. This is for use in my home so mainly used for media files (video, music, movies, photos, applications, stuff) and some business backup ups and personal documentation so it's not a heavily used device. I am still running my original Synology DS410J but this device is no longer supported within the DSM upgrade program and it's 85% full so my plan was to go to a 1515+ and add some new drives. I only have a Gigabyte network so frankly SSD would be a waste based on above so will go old school, high capacity HD's.
The device does support 5 drives, so I could use an SSD for Cache purposes perhaps, best of both worlds approach or again wasted effort for no real benefit?