I consider them complimetary products. BESR is more focused on disaster recovery, but you can extract individual files and folders from the images. The image browser works well and extracts individual files and folders well too. IMHO, the separate feature for file and folder backups in BESR are not as good as BEWS, (or NTBACKUP for that matter) but you could "get by" with it.
In my environment, I use BESR to capture disaster reovery images at least once per week. I use BEWS for daily backups. After recovering an entire system with BESR, I use BEWS to restore the data to the most recent versions captured in the daily backups.
Both products do have the capability to do incremental backups if disk space usage is a consideration. You could use BESR as a standalone backup solution if your backup needs are simple and do not need granular recovery of SQL or Exchange databases. Yes, BESR does have an option for granular restoration of Exchange Mailboxes/Items and SharePoint items. The GRT option has come a long way, but there are still folks who are having trouble with it. I still consider it a work in progress. If you have Public Folders in your Exchange environment, GRT can't recover those, but BEWS can with the Exchange agent installed.