Well...the way the Datto Alto works, think of it as a NAS....but with an interface. Backups go to it..and then it replicates offsite. Plus it can virtualize offsite and bring the servers services down to the local network through a secure VPN tunnel if the server happens to catch fire and melt into a puddle of steel and plastic.
Dattos Siris backup product is a few notches higher, it does local virtualization and can handle many more servers and workstations..the Alto is only for a max of 2x devices to be backed up.
If you don't want the security of virtualizing a backup wrapped up in one appliance or service...I have done a primitive setup of what Datto is loosely based on....get a Synology NAS on the network..and use StorageCrafts SBS product to backup to it. If you want to come up with your own offsite replication, they have a separate product called ImageManager which you can configure to do those things.
DattoBackup utilizes Storagecraft Shadowprotect. They've hired a few StorageCraft employees....recently onboarding Storagecrafts eastern US rep. I have a feeling they may totally pickup Storagecraft in a few years.